<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:019d8775-55b7-7fd0-ae08-79d3840a0df3,g:3580ce59-51cf-4c3c-8e7f-1e844c0352bb-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://www.unum.com/role/DocumentandEntityInformation" xlink:type="simple" xlink:href="unm-20260331.xsd#DocumentandEntityInformation"/>
  <link:definitionLink xlink:role="http://www.unum.com/role/DocumentandEntityInformation" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityInformationLineItems_019d8775-5d3f-713b-aff4-1c8a1e4816d1" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitiesTable_019d8775-5d3f-7868-a5f2-e33abc0332da" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntitiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dei_EntityInformationLineItems_019d8775-5d3f-713b-aff4-1c8a1e4816d1" xlink:to="loc_dei_EntitiesTable_019d8775-5d3f-7868-a5f2-e33abc0332da" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityListingsExchangeAxis_019d8775-5d3f-75fb-9de5-1ecd0dccf6ba" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityListingsExchangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_EntitiesTable_019d8775-5d3f-7868-a5f2-e33abc0332da" xlink:to="loc_dei_EntityListingsExchangeAxis_019d8775-5d3f-75fb-9de5-1ecd0dccf6ba" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_ExchangeDomain_019d8775-5d3f-75fb-9de5-1ecd0dccf6ba_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_ExchangeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_EntityListingsExchangeAxis_019d8775-5d3f-75fb-9de5-1ecd0dccf6ba" xlink:to="loc_dei_ExchangeDomain_019d8775-5d3f-75fb-9de5-1ecd0dccf6ba_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_ExchangeDomain_019d8775-5d3f-7a30-825f-39614780a097" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_ExchangeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_EntityListingsExchangeAxis_019d8775-5d3f-75fb-9de5-1ecd0dccf6ba" xlink:to="loc_dei_ExchangeDomain_019d8775-5d3f-7a30-825f-39614780a097" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_exch_XNYS_019d8775-5d3f-7391-9bb2-6864cd66d93a" xlink:href="https://xbrl.sec.gov/exch/2026/exch-2026.xsd#exch_XNYS"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_ExchangeDomain_019d8775-5d3f-7a30-825f-39614780a097" xlink:to="loc_exch_XNYS_019d8775-5d3f-7391-9bb2-6864cd66d93a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019d8775-5d3f-771d-9011-87d0cd009693" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_EntitiesTable_019d8775-5d3f-7868-a5f2-e33abc0332da" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019d8775-5d3f-771d-9011-87d0cd009693" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019d8775-5d3f-771d-9011-87d0cd009693_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019d8775-5d3f-771d-9011-87d0cd009693" xlink:to="loc_us-gaap_ClassOfStockDomain_019d8775-5d3f-771d-9011-87d0cd009693_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019d8775-5d3f-7185-9d46-377abf83f4f4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019d8775-5d3f-771d-9011-87d0cd009693" xlink:to="loc_us-gaap_ClassOfStockDomain_019d8775-5d3f-7185-9d46-377abf83f4f4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_019d8775-5d3f-7040-baf4-8381f632b0c0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019d8775-5d3f-7185-9d46-377abf83f4f4" xlink:to="loc_us-gaap_CommonClassAMember_019d8775-5d3f-7040-baf4-8381f632b0c0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_A6250JuniorSubordinatedNotesDue2058Member_019d8775-5d3f-7a0f-9285-7637da6e4a55" xlink:href="unm-20260331.xsd#unm_A6250JuniorSubordinatedNotesDue2058Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019d8775-5d3f-7185-9d46-377abf83f4f4" xlink:to="loc_unm_A6250JuniorSubordinatedNotesDue2058Member_019d8775-5d3f-7a0f-9285-7637da6e4a55" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentType_019d8775-5d3f-7cd6-b791-65a5da1418b2" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentType"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019d8775-5d3f-713b-aff4-1c8a1e4816d1" xlink:to="loc_dei_DocumentType_019d8775-5d3f-7cd6-b791-65a5da1418b2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentQuarterlyReport_019d8775-5d3f-7e2b-8773-03b521082825" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentQuarterlyReport"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019d8775-5d3f-713b-aff4-1c8a1e4816d1" xlink:to="loc_dei_DocumentQuarterlyReport_019d8775-5d3f-7e2b-8773-03b521082825" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AmendmentFlag_019d8775-5d3f-7e30-b277-35982634e5a0" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_AmendmentFlag"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019d8775-5d3f-713b-aff4-1c8a1e4816d1" xlink:to="loc_dei_AmendmentFlag_019d8775-5d3f-7e30-b277-35982634e5a0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentPeriodEndDate_019d8775-5d3f-7818-b3b0-e91cfd5b9d1d" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentPeriodEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019d8775-5d3f-713b-aff4-1c8a1e4816d1" xlink:to="loc_dei_DocumentPeriodEndDate_019d8775-5d3f-7818-b3b0-e91cfd5b9d1d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalYearFocus_019d8775-5d3f-795d-83ff-f6270615ab21" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentFiscalYearFocus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019d8775-5d3f-713b-aff4-1c8a1e4816d1" xlink:to="loc_dei_DocumentFiscalYearFocus_019d8775-5d3f-795d-83ff-f6270615ab21" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CurrentFiscalYearEndDate_019d8775-5d3f-7b81-8ed1-38efffc831fd" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_CurrentFiscalYearEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019d8775-5d3f-713b-aff4-1c8a1e4816d1" xlink:to="loc_dei_CurrentFiscalYearEndDate_019d8775-5d3f-7b81-8ed1-38efffc831fd" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalPeriodFocus_019d8775-5d3f-731e-8007-c3a77843089a" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentFiscalPeriodFocus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019d8775-5d3f-713b-aff4-1c8a1e4816d1" xlink:to="loc_dei_DocumentFiscalPeriodFocus_019d8775-5d3f-731e-8007-c3a77843089a" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentTransitionReport_019d8775-5d3f-78ac-b171-d179c04298ff" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentTransitionReport"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019d8775-5d3f-713b-aff4-1c8a1e4816d1" xlink:to="loc_dei_DocumentTransitionReport_019d8775-5d3f-78ac-b171-d179c04298ff" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFileNumber_019d8775-5d3f-7384-8ec7-19328dcdfaa3" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityFileNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019d8775-5d3f-713b-aff4-1c8a1e4816d1" xlink:to="loc_dei_EntityFileNumber_019d8775-5d3f-7384-8ec7-19328dcdfaa3" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityRegistrantName_019d8775-5d3f-7238-966f-cff9b7e7f817" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityRegistrantName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019d8775-5d3f-713b-aff4-1c8a1e4816d1" xlink:to="loc_dei_EntityRegistrantName_019d8775-5d3f-7238-966f-cff9b7e7f817" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCentralIndexKey_019d8775-5d3f-73a4-9bf4-7c982be2d8a9" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityCentralIndexKey"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019d8775-5d3f-713b-aff4-1c8a1e4816d1" xlink:to="loc_dei_EntityCentralIndexKey_019d8775-5d3f-73a4-9bf4-7c982be2d8a9" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityIncorporationStateCountryCode_019d8775-5d3f-78e6-be1e-6a9b01ffa588" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityIncorporationStateCountryCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019d8775-5d3f-713b-aff4-1c8a1e4816d1" xlink:to="loc_dei_EntityIncorporationStateCountryCode_019d8775-5d3f-78e6-be1e-6a9b01ffa588" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityTaxIdentificationNumber_019d8775-5d3f-7b1e-b9eb-6ee2ff9097a7" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityTaxIdentificationNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019d8775-5d3f-713b-aff4-1c8a1e4816d1" xlink:to="loc_dei_EntityTaxIdentificationNumber_019d8775-5d3f-7b1e-b9eb-6ee2ff9097a7" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine1_019d8775-5d3f-7722-9379-453e0b5341c3" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressAddressLine1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019d8775-5d3f-713b-aff4-1c8a1e4816d1" xlink:to="loc_dei_EntityAddressAddressLine1_019d8775-5d3f-7722-9379-453e0b5341c3" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressCityOrTown_019d8775-5d3f-78d8-a2c0-b626c892054b" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressCityOrTown"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019d8775-5d3f-713b-aff4-1c8a1e4816d1" xlink:to="loc_dei_EntityAddressCityOrTown_019d8775-5d3f-78d8-a2c0-b626c892054b" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressStateOrProvince_019d8775-5d3f-7730-9dd3-9f2870a9d92d" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressStateOrProvince"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019d8775-5d3f-713b-aff4-1c8a1e4816d1" xlink:to="loc_dei_EntityAddressStateOrProvince_019d8775-5d3f-7730-9dd3-9f2870a9d92d" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressPostalZipCode_019d8775-5d3f-7a2c-ae66-f7f870755d54" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressPostalZipCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019d8775-5d3f-713b-aff4-1c8a1e4816d1" xlink:to="loc_dei_EntityAddressPostalZipCode_019d8775-5d3f-7a2c-ae66-f7f870755d54" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CityAreaCode_019d8775-5d3f-79b5-bb3a-3a9b8236ef89" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_CityAreaCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019d8775-5d3f-713b-aff4-1c8a1e4816d1" xlink:to="loc_dei_CityAreaCode_019d8775-5d3f-79b5-bb3a-3a9b8236ef89" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LocalPhoneNumber_019d8775-5d3f-7f4f-a409-0e0c817380eb" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LocalPhoneNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019d8775-5d3f-713b-aff4-1c8a1e4816d1" xlink:to="loc_dei_LocalPhoneNumber_019d8775-5d3f-7f4f-a409-0e0c817380eb" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_Security12bTitle_019d8775-5d3f-7159-8652-e803466bed4a" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_Security12bTitle"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019d8775-5d3f-713b-aff4-1c8a1e4816d1" xlink:to="loc_dei_Security12bTitle_019d8775-5d3f-7159-8652-e803466bed4a" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_TradingSymbol_019d8775-5d3f-743c-a497-b7fbc20d3703" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_TradingSymbol"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019d8775-5d3f-713b-aff4-1c8a1e4816d1" xlink:to="loc_dei_TradingSymbol_019d8775-5d3f-743c-a497-b7fbc20d3703" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SecurityExchangeName_019d8775-5d3f-7585-9d3a-8f68fad5fe9b" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_SecurityExchangeName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019d8775-5d3f-713b-aff4-1c8a1e4816d1" xlink:to="loc_dei_SecurityExchangeName_019d8775-5d3f-7585-9d3a-8f68fad5fe9b" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCurrentReportingStatus_019d8775-5d3f-7721-8fe5-964c173da429" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityCurrentReportingStatus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019d8775-5d3f-713b-aff4-1c8a1e4816d1" xlink:to="loc_dei_EntityCurrentReportingStatus_019d8775-5d3f-7721-8fe5-964c173da429" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityInteractiveDataCurrent_019d8775-5d3f-7b51-b0b4-ae0d9a475b65" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityInteractiveDataCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019d8775-5d3f-713b-aff4-1c8a1e4816d1" xlink:to="loc_dei_EntityInteractiveDataCurrent_019d8775-5d3f-7b51-b0b4-ae0d9a475b65" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFilerCategory_019d8775-5d3f-7b43-a798-ccb04bb92c4b" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityFilerCategory"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019d8775-5d3f-713b-aff4-1c8a1e4816d1" xlink:to="loc_dei_EntityFilerCategory_019d8775-5d3f-7b43-a798-ccb04bb92c4b" xlink:type="arc" order="24"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitySmallBusiness_019d8775-5d3f-7ee2-904f-e36c3d42d133" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntitySmallBusiness"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019d8775-5d3f-713b-aff4-1c8a1e4816d1" xlink:to="loc_dei_EntitySmallBusiness_019d8775-5d3f-7ee2-904f-e36c3d42d133" xlink:type="arc" order="25"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityEmergingGrowthCompany_019d8775-5d3f-7b3d-a7ac-978b7b2d730a" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityEmergingGrowthCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019d8775-5d3f-713b-aff4-1c8a1e4816d1" xlink:to="loc_dei_EntityEmergingGrowthCompany_019d8775-5d3f-7b3d-a7ac-978b7b2d730a" xlink:type="arc" order="26"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityShellCompany_019d8775-5d3f-77a6-a797-91d83b43ff66" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityShellCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019d8775-5d3f-713b-aff4-1c8a1e4816d1" xlink:to="loc_dei_EntityShellCompany_019d8775-5d3f-77a6-a797-91d83b43ff66" xlink:type="arc" order="27"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCommonStockSharesOutstanding_019d8775-5d3f-764e-b012-6da70d35d2ca" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityCommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019d8775-5d3f-713b-aff4-1c8a1e4816d1" xlink:to="loc_dei_EntityCommonStockSharesOutstanding_019d8775-5d3f-764e-b012-6da70d35d2ca" xlink:type="arc" order="28"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.unum.com/role/CONSOLIDATEDSTATEMENTSOFSTOCKHOLDERSEQUITY" xlink:type="simple" xlink:href="unm-20260331.xsd#CONSOLIDATEDSTATEMENTSOFSTOCKHOLDERSEQUITY"/>
  <link:definitionLink xlink:role="http://www.unum.com/role/CONSOLIDATEDSTATEMENTSOFSTOCKHOLDERSEQUITY" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019d8775-5d3f-70f1-82e3-75d5828f9b0d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019d8775-5d3f-7443-9aaf-2589b4a8ed64" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019d8775-5d3f-70f1-82e3-75d5828f9b0d" xlink:to="loc_us-gaap_StatementTable_019d8775-5d3f-7443-9aaf-2589b4a8ed64" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019d8775-5d3f-7996-863e-128e1a3969a5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019d8775-5d3f-7443-9aaf-2589b4a8ed64" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019d8775-5d3f-7996-863e-128e1a3969a5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019d8775-5d3f-7996-863e-128e1a3969a5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019d8775-5d3f-7996-863e-128e1a3969a5" xlink:to="loc_us-gaap_EquityComponentDomain_019d8775-5d3f-7996-863e-128e1a3969a5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019d8775-5d3f-7019-8bab-44cc597fe368" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019d8775-5d3f-7996-863e-128e1a3969a5" xlink:to="loc_us-gaap_EquityComponentDomain_019d8775-5d3f-7019-8bab-44cc597fe368" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019d8775-5d3f-72fd-b212-000806e17570" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019d8775-5d3f-7019-8bab-44cc597fe368" xlink:to="loc_us-gaap_CommonStockMember_019d8775-5d3f-72fd-b212-000806e17570" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_019d8775-5d3f-7f8d-a447-5449370276c2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019d8775-5d3f-7019-8bab-44cc597fe368" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_019d8775-5d3f-7f8d-a447-5449370276c2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019d8775-5d3f-7a6c-9c84-18f5f1382383" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019d8775-5d3f-7019-8bab-44cc597fe368" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019d8775-5d3f-7a6c-9c84-18f5f1382383" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_019d8775-5d3f-7151-b28d-b82cbc6777e3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019d8775-5d3f-7019-8bab-44cc597fe368" xlink:to="loc_us-gaap_RetainedEarningsMember_019d8775-5d3f-7151-b28d-b82cbc6777e3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockCommonMember_019d8775-5d3f-78f6-a6ef-5360751e9875" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TreasuryStockCommonMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019d8775-5d3f-7019-8bab-44cc597fe368" xlink:to="loc_us-gaap_TreasuryStockCommonMember_019d8775-5d3f-78f6-a6ef-5360751e9875" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019d8775-5d3f-7ea8-baa7-daf68de5401b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019d8775-5d3f-70f1-82e3-75d5828f9b0d" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019d8775-5d3f-7ea8-baa7-daf68de5401b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_019d8775-5d3f-7ef4-97d8-3ca3bcc06622" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019d8775-5d3f-7ea8-baa7-daf68de5401b" xlink:to="loc_us-gaap_StockholdersEquity_019d8775-5d3f-7ef4-97d8-3ca3bcc06622" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_019d8775-5d3f-7468-9290-8f21cf7a49c7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodValueNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019d8775-5d3f-7ea8-baa7-daf68de5401b" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_019d8775-5d3f-7468-9290-8f21cf7a49c7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockValueAcquiredCostMethod_019d8775-5d3f-7bac-9474-2e111d4f437a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TreasuryStockValueAcquiredCostMethod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019d8775-5d3f-7ea8-baa7-daf68de5401b" xlink:to="loc_us-gaap_TreasuryStockValueAcquiredCostMethod_019d8775-5d3f-7bac-9474-2e111d4f437a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_019d8775-5d3f-7fb4-a8ff-dd3ffc3359bc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019d8775-5d3f-7ea8-baa7-daf68de5401b" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_019d8775-5d3f-7fb4-a8ff-dd3ffc3359bc" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019d8775-5d3f-778f-ac4c-6eb6206e4a06" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019d8775-5d3f-7ea8-baa7-daf68de5401b" xlink:to="loc_us-gaap_NetIncomeLoss_019d8775-5d3f-778f-ac4c-6eb6206e4a06" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsCash_019d8775-5d3f-740a-9608-cd20775f6f59" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DividendsCash"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019d8775-5d3f-7ea8-baa7-daf68de5401b" xlink:to="loc_us-gaap_DividendsCash_019d8775-5d3f-740a-9608-cd20775f6f59" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_019d8775-5d3f-7840-853c-101cb2e778ee" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquity"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.unum.com/role/FairValuesofFinancialInstrumentsPrivateEquityPartnershipsDetails" xlink:type="simple" xlink:href="unm-20260331.xsd#FairValuesofFinancialInstrumentsPrivateEquityPartnershipsDetails"/>
  <link:definitionLink xlink:role="http://www.unum.com/role/FairValuesofFinancialInstrumentsPrivateEquityPartnershipsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareLineItems_019d8775-5d3f-7e92-91d9-06b60ad209cd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareTable_019d8775-5d3f-70a9-b587-d560e51f696b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareLineItems_019d8775-5d3f-7e92-91d9-06b60ad209cd" xlink:to="loc_us-gaap_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareTable_019d8775-5d3f-70a9-b587-d560e51f696b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_019d8775-5d3f-7f55-9950-d02581c5ce24" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareTable_019d8775-5d3f-70a9-b587-d560e51f696b" xlink:to="loc_us-gaap_FinancialInstrumentAxis_019d8775-5d3f-7f55-9950-d02581c5ce24" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5d3f-7f55-9950-d02581c5ce24_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019d8775-5d3f-7f55-9950-d02581c5ce24" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5d3f-7f55-9950-d02581c5ce24_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5d3f-77ee-9b20-8417d988a8b3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019d8775-5d3f-7f55-9950-d02581c5ce24" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5d3f-77ee-9b20-8417d988a8b3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PrivateEquityFundsMember_019d8775-5d3f-750b-a882-5d03a1de1243" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PrivateEquityFundsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5d3f-77ee-9b20-8417d988a8b3" xlink:to="loc_us-gaap_PrivateEquityFundsMember_019d8775-5d3f-750b-a882-5d03a1de1243" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_PrivateEquityFundTypeAxis_019d8775-5d3f-702a-874b-b27810446727" xlink:href="unm-20260331.xsd#unm_PrivateEquityFundTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareTable_019d8775-5d3f-70a9-b587-d560e51f696b" xlink:to="loc_unm_PrivateEquityFundTypeAxis_019d8775-5d3f-702a-874b-b27810446727" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_PrivateEquityFundTypeDomain_019d8775-5d3f-702a-874b-b27810446727_default" xlink:href="unm-20260331.xsd#unm_PrivateEquityFundTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_unm_PrivateEquityFundTypeAxis_019d8775-5d3f-702a-874b-b27810446727" xlink:to="loc_unm_PrivateEquityFundTypeDomain_019d8775-5d3f-702a-874b-b27810446727_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_PrivateEquityFundTypeDomain_019d8775-5d3f-779c-ab16-f52a768beeba" xlink:href="unm-20260331.xsd#unm_PrivateEquityFundTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_unm_PrivateEquityFundTypeAxis_019d8775-5d3f-702a-874b-b27810446727" xlink:to="loc_unm_PrivateEquityFundTypeDomain_019d8775-5d3f-779c-ab16-f52a768beeba" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_PrivateCreditMember_019d8775-5d3f-7980-82a1-1ae67de225c3" xlink:href="unm-20260331.xsd#unm_PrivateCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_unm_PrivateEquityFundTypeDomain_019d8775-5d3f-779c-ab16-f52a768beeba" xlink:to="loc_unm_PrivateCreditMember_019d8775-5d3f-7980-82a1-1ae67de225c3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_PrivateEquityLimitedPartnershipMember_019d8775-5d3f-76f8-8679-b15c4661a0ec" xlink:href="unm-20260331.xsd#unm_PrivateEquityLimitedPartnershipMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_unm_PrivateEquityFundTypeDomain_019d8775-5d3f-779c-ab16-f52a768beeba" xlink:to="loc_unm_PrivateEquityLimitedPartnershipMember_019d8775-5d3f-76f8-8679-b15c4661a0ec" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_RealAssetsMember_019d8775-5d3f-7062-81df-abe78832e33f" xlink:href="unm-20260331.xsd#unm_RealAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_unm_PrivateEquityFundTypeDomain_019d8775-5d3f-779c-ab16-f52a768beeba" xlink:to="loc_unm_RealAssetsMember_019d8775-5d3f-7062-81df-abe78832e33f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_RedemptionTermAxis_019d8775-5d3f-7ea8-8de9-43669596386a" xlink:href="unm-20260331.xsd#unm_RedemptionTermAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareTable_019d8775-5d3f-70a9-b587-d560e51f696b" xlink:to="loc_unm_RedemptionTermAxis_019d8775-5d3f-7ea8-8de9-43669596386a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_RedemptionTermDomain_019d8775-5d3f-7ea8-8de9-43669596386a_default" xlink:href="unm-20260331.xsd#unm_RedemptionTermDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_unm_RedemptionTermAxis_019d8775-5d3f-7ea8-8de9-43669596386a" xlink:to="loc_unm_RedemptionTermDomain_019d8775-5d3f-7ea8-8de9-43669596386a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_RedemptionTermDomain_019d8775-5d3f-71f3-9e1e-5513c381db26" xlink:href="unm-20260331.xsd#unm_RedemptionTermDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_unm_RedemptionTermAxis_019d8775-5d3f-7ea8-8de9-43669596386a" xlink:to="loc_unm_RedemptionTermDomain_019d8775-5d3f-71f3-9e1e-5513c381db26" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_NotRedeemableMember_019d8775-5d3f-7644-b118-0f0e8c187b5b" xlink:href="unm-20260331.xsd#unm_NotRedeemableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_unm_RedemptionTermDomain_019d8775-5d3f-71f3-9e1e-5513c381db26" xlink:to="loc_unm_NotRedeemableMember_019d8775-5d3f-7644-b118-0f0e8c187b5b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_Quarterly90DaysNoticeMember_019dbbae-755f-7ec0-b201-2196293f12e0" xlink:href="unm-20260331.xsd#unm_Quarterly90DaysNoticeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_unm_RedemptionTermDomain_019d8775-5d3f-71f3-9e1e-5513c381db26" xlink:to="loc_unm_Quarterly90DaysNoticeMember_019dbbae-755f-7ec0-b201-2196293f12e0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_QuarterlyAfter55YearLockWith90DaysNoticeMember_019d8775-5d3f-7ad4-b916-be529fdf4002" xlink:href="unm-20260331.xsd#unm_QuarterlyAfter55YearLockWith90DaysNoticeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_unm_RedemptionTermDomain_019d8775-5d3f-71f3-9e1e-5513c381db26" xlink:to="loc_unm_QuarterlyAfter55YearLockWith90DaysNoticeMember_019d8775-5d3f-7ad4-b916-be529fdf4002" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AlternativeInvestment_019d8775-5d3f-74cd-a770-5dbd8684bcb0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AlternativeInvestment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareLineItems_019d8775-5d3f-7e92-91d9-06b60ad209cd" xlink:to="loc_us-gaap_AlternativeInvestment_019d8775-5d3f-74cd-a770-5dbd8684bcb0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareUnfundedCommittments_019d8775-5d3f-7bd3-9af1-2a4965dd2c0d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareUnfundedCommittments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareLineItems_019d8775-5d3f-7e92-91d9-06b60ad209cd" xlink:to="loc_us-gaap_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareUnfundedCommittments_019d8775-5d3f-7bd3-9af1-2a4965dd2c0d" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.unum.com/role/FairValueMeasurementsbyInputLevelDetail" xlink:type="simple" xlink:href="unm-20260331.xsd#FairValueMeasurementsbyInputLevelDetail"/>
  <link:definitionLink xlink:role="http://www.unum.com/role/FairValueMeasurementsbyInputLevelDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019d8775-5d40-7e50-b0a8-84325ab4fa21" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019d8775-5d3f-7065-9530-d3faa3bd6a8a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019d8775-5d40-7e50-b0a8-84325ab4fa21" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019d8775-5d3f-7065-9530-d3faa3bd6a8a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_019d8775-5d3f-7b30-be70-aea0c69596eb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019d8775-5d3f-7065-9530-d3faa3bd6a8a" xlink:to="loc_us-gaap_FinancialInstrumentAxis_019d8775-5d3f-7b30-be70-aea0c69596eb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5d3f-7b30-be70-aea0c69596eb_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019d8775-5d3f-7b30-be70-aea0c69596eb" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5d3f-7b30-be70-aea0c69596eb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5d3f-746a-a683-99a7fb4c679b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019d8775-5d3f-7b30-be70-aea0c69596eb" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5d3f-746a-a683-99a7fb4c679b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USTreasuryAndGovernmentMember_019d8775-5d3f-7ae5-b2a0-8dcf754944a4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_USTreasuryAndGovernmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5d3f-746a-a683-99a7fb4c679b" xlink:to="loc_us-gaap_USTreasuryAndGovernmentMember_019d8775-5d3f-7ae5-b2a0-8dcf754944a4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USStatesAndPoliticalSubdivisionsMember_019d8775-5d3f-72a7-8af9-31387276b76d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_USStatesAndPoliticalSubdivisionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5d3f-746a-a683-99a7fb4c679b" xlink:to="loc_us-gaap_USStatesAndPoliticalSubdivisionsMember_019d8775-5d3f-72a7-8af9-31387276b76d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignGovernmentDebtSecuritiesMember_019d8775-5d3f-7c20-8a86-5acf0ed0343b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ForeignGovernmentDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5d3f-746a-a683-99a7fb4c679b" xlink:to="loc_us-gaap_ForeignGovernmentDebtSecuritiesMember_019d8775-5d3f-7c20-8a86-5acf0ed0343b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PublicUtilityBondsMember_019d8775-5d3f-75a4-8544-425e4e1535f3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PublicUtilityBondsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5d3f-746a-a683-99a7fb4c679b" xlink:to="loc_us-gaap_PublicUtilityBondsMember_019d8775-5d3f-75a4-8544-425e4e1535f3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetBackedSecuritiesMember_019d8775-5d3f-7f98-9a19-c7bcadc1e381" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetBackedSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5d3f-746a-a683-99a7fb4c679b" xlink:to="loc_us-gaap_AssetBackedSecuritiesMember_019d8775-5d3f-7f98-9a19-c7bcadc1e381" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateDebtSecuritiesMember_019d8775-5d3f-7e04-b851-de0b9f4f7eec" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CorporateDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5d3f-746a-a683-99a7fb4c679b" xlink:to="loc_us-gaap_CorporateDebtSecuritiesMember_019d8775-5d3f-7e04-b851-de0b9f4f7eec" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RedeemablePreferredStockMember_019d8775-5d3f-788f-8adc-c2e71e091a08" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RedeemablePreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5d3f-746a-a683-99a7fb4c679b" xlink:to="loc_us-gaap_RedeemablePreferredStockMember_019d8775-5d3f-788f-8adc-c2e71e091a08" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PrivateEquityFundsMember_019d8775-5d3f-76bd-92ef-7146d31e732e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PrivateEquityFundsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5d3f-746a-a683-99a7fb4c679b" xlink:to="loc_us-gaap_PrivateEquityFundsMember_019d8775-5d3f-76bd-92ef-7146d31e732e" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementFrequencyAxis_019d8775-5d3f-7b1b-9598-13d58dfee99f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByMeasurementFrequencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019d8775-5d3f-7065-9530-d3faa3bd6a8a" xlink:to="loc_us-gaap_FairValueByMeasurementFrequencyAxis_019d8775-5d3f-7b1b-9598-13d58dfee99f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_019d8775-5d3f-7b1b-9598-13d58dfee99f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_019d8775-5d3f-7b1b-9598-13d58dfee99f" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_019d8775-5d3f-7b1b-9598-13d58dfee99f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_019d8775-5d3f-7df8-972e-06226c36c1da" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_019d8775-5d3f-7b1b-9598-13d58dfee99f" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_019d8775-5d3f-7df8-972e-06226c36c1da" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsRecurringMember_019d8775-5d3f-7d94-b25c-f9c98787c147" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsRecurringMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementFrequencyDomain_019d8775-5d3f-7df8-972e-06226c36c1da" xlink:to="loc_us-gaap_FairValueMeasurementsRecurringMember_019d8775-5d3f-7d94-b25c-f9c98787c147" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019d8775-5d3f-7e8f-8c51-3afe734e5b3f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019d8775-5d3f-7065-9530-d3faa3bd6a8a" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019d8775-5d3f-7e8f-8c51-3afe734e5b3f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019d8775-5d3f-7e8f-8c51-3afe734e5b3f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019d8775-5d3f-7e8f-8c51-3afe734e5b3f" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019d8775-5d3f-7e8f-8c51-3afe734e5b3f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019d8775-5d3f-74a9-81c8-eb878fb1820c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019d8775-5d3f-7e8f-8c51-3afe734e5b3f" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019d8775-5d3f-74a9-81c8-eb878fb1820c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_019d8775-5d3f-77de-97b1-e450dc6a4cdc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019d8775-5d3f-74a9-81c8-eb878fb1820c" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_019d8775-5d3f-77de-97b1-e450dc6a4cdc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_019d8775-5d40-7fb3-a072-34777af94479" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019d8775-5d3f-74a9-81c8-eb878fb1820c" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_019d8775-5d40-7fb3-a072-34777af94479" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_019d8775-5d40-7094-bd67-e48693e7dded" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019d8775-5d3f-74a9-81c8-eb878fb1820c" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_019d8775-5d40-7094-bd67-e48693e7dded" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasuredAtNetAssetValuePerShareMember_019d8775-5d40-7319-a01c-e1bb057197ae" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasuredAtNetAssetValuePerShareMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019d8775-5d3f-74a9-81c8-eb878fb1820c" xlink:to="loc_us-gaap_FairValueMeasuredAtNetAssetValuePerShareMember_019d8775-5d40-7319-a01c-e1bb057197ae" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_019d8775-5d40-7499-9366-14bdd4782655" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019d8775-5d3f-7065-9530-d3faa3bd6a8a" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_019d8775-5d40-7499-9366-14bdd4782655" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5d40-7499-9366-14bdd4782655_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019d8775-5d40-7499-9366-14bdd4782655" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5d40-7499-9366-14bdd4782655_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5d40-76b5-ab00-aad4792f086d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019d8775-5d40-7499-9366-14bdd4782655" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5d40-76b5-ab00-aad4792f086d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForwardContractsMember_019d8775-5d40-76a6-983b-07229948b03f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ForwardContractsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5d40-76b5-ab00-aad4792f086d" xlink:to="loc_us-gaap_ForwardContractsMember_019d8775-5d40-76a6-983b-07229948b03f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CurrencySwapMember_019d8775-5d40-7705-956f-3595ca4c0cee" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CurrencySwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5d40-76b5-ab00-aad4792f086d" xlink:to="loc_us-gaap_CurrencySwapMember_019d8775-5d40-7705-956f-3595ca4c0cee" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmbeddedDerivativeFinancialInstrumentsMember_019d8775-5d40-7839-b51f-61ee600ff99f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmbeddedDerivativeFinancialInstrumentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5d40-76b5-ab00-aad4792f086d" xlink:to="loc_us-gaap_EmbeddedDerivativeFinancialInstrumentsMember_019d8775-5d40-7839-b51f-61ee600ff99f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsAbstract_019d8775-5d40-77a0-9836-4ed6e952a024" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019d8775-5d40-7e50-b0a8-84325ab4fa21" xlink:to="loc_us-gaap_AssetsAbstract_019d8775-5d40-77a0-9836-4ed6e952a024" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_019d8775-5d40-72f1-b7e3-9b2046f5e2ab" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019d8775-5d40-77a0-9836-4ed6e952a024" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_019d8775-5d40-72f1-b7e3-9b2046f5e2ab" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesFvNi_019d8775-5d40-751a-bb2a-a0a4d168627d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquitySecuritiesFvNi"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019d8775-5d40-77a0-9836-4ed6e952a024" xlink:to="loc_us-gaap_EquitySecuritiesFvNi_019d8775-5d40-751a-bb2a-a0a4d168627d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AlternativeInvestment_019d8775-5d40-76c6-be28-305e636f519d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AlternativeInvestment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019d8775-5d40-77a0-9836-4ed6e952a024" xlink:to="loc_us-gaap_AlternativeInvestment_019d8775-5d40-76c6-be28-305e636f519d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLongTermInvestments_019d8775-5d40-7a2a-accf-f23cef694d83" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherLongTermInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019d8775-5d40-77a0-9836-4ed6e952a024" xlink:to="loc_us-gaap_OtherLongTermInvestments_019d8775-5d40-7a2a-accf-f23cef694d83" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssetStatementOfFinancialPositionExtensibleEnumeration_019d8775-5d40-79c3-871b-a5c192b18d9e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeAssetStatementOfFinancialPositionExtensibleEnumeration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019d8775-5d40-77a0-9836-4ed6e952a024" xlink:to="loc_us-gaap_DerivativeAssetStatementOfFinancialPositionExtensibleEnumeration_019d8775-5d40-79c3-871b-a5c192b18d9e" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssets_019d8775-5d40-7aa1-be1e-61f26fb5f474" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019d8775-5d40-77a0-9836-4ed6e952a024" xlink:to="loc_us-gaap_DerivativeAssets_019d8775-5d40-7aa1-be1e-61f26fb5f474" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosure_019d8775-5d40-7799-9182-6b77d9025edd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019d8775-5d40-77a0-9836-4ed6e952a024" xlink:to="loc_us-gaap_AssetsFairValueDisclosure_019d8775-5d40-7799-9182-6b77d9025edd" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAbstract_019d8775-5d40-74c4-8b02-b47654b09bf6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019d8775-5d40-7e50-b0a8-84325ab4fa21" xlink:to="loc_us-gaap_LiabilitiesAbstract_019d8775-5d40-74c4-8b02-b47654b09bf6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLiabilityStatementOfFinancialPositionExtensibleEnumeration_019d8775-5d40-7000-90fe-d28c6ba12e5c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeLiabilityStatementOfFinancialPositionExtensibleEnumeration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_019d8775-5d40-74c4-8b02-b47654b09bf6" xlink:to="loc_us-gaap_DerivativeLiabilityStatementOfFinancialPositionExtensibleEnumeration_019d8775-5d40-7000-90fe-d28c6ba12e5c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLiabilities_019d8775-5d40-7af3-943b-a038b1dc59e6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_019d8775-5d40-74c4-8b02-b47654b09bf6" xlink:to="loc_us-gaap_DerivativeLiabilities_019d8775-5d40-7af3-943b-a038b1dc59e6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesFairValueDisclosure_019d8775-5d40-7753-986b-faf7cd157427" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_019d8775-5d40-74c4-8b02-b47654b09bf6" xlink:to="loc_us-gaap_LiabilitiesFairValueDisclosure_019d8775-5d40-7753-986b-faf7cd157427" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.unum.com/role/ChangesinAssetsandLiabilitiesMeasuredatFairValueonaRecurringBasisusingSignificantUnobservableInputsLevel3Detail" xlink:type="simple" xlink:href="unm-20260331.xsd#ChangesinAssetsandLiabilitiesMeasuredatFairValueonaRecurringBasisusingSignificantUnobservableInputsLevel3Detail"/>
  <link:definitionLink xlink:role="http://www.unum.com/role/ChangesinAssetsandLiabilitiesMeasuredatFairValueonaRecurringBasisusingSignificantUnobservableInputsLevel3Detail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019d8775-5d40-74ec-b514-062da6bbdd66" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_019d8775-5d40-76ef-a3d0-0ab769b656bb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019d8775-5d40-74ec-b514-062da6bbdd66" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_019d8775-5d40-76ef-a3d0-0ab769b656bb" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByAssetClassAxis_019d8775-5d40-786b-af88-125c680b2ade" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByAssetClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_019d8775-5d40-76ef-a3d0-0ab769b656bb" xlink:to="loc_us-gaap_FairValueByAssetClassAxis_019d8775-5d40-786b-af88-125c680b2ade" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019d8775-5d40-786b-af88-125c680b2ade_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByAssetClassAxis_019d8775-5d40-786b-af88-125c680b2ade" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019d8775-5d40-786b-af88-125c680b2ade_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019d8775-5d40-7b32-a43f-365b0fa23675" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByAssetClassAxis_019d8775-5d40-786b-af88-125c680b2ade" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019d8775-5d40-7b32-a43f-365b0fa23675" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PublicUtilityBondsMember_019d8775-5d40-7ce5-a3e3-137a2e12c958" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PublicUtilityBondsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019d8775-5d40-7b32-a43f-365b0fa23675" xlink:to="loc_us-gaap_PublicUtilityBondsMember_019d8775-5d40-7ce5-a3e3-137a2e12c958" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetBackedSecuritiesMember_019d8775-5d40-7f2c-99b8-c12b32976e73" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetBackedSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019d8775-5d40-7b32-a43f-365b0fa23675" xlink:to="loc_us-gaap_AssetBackedSecuritiesMember_019d8775-5d40-7f2c-99b8-c12b32976e73" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateDebtSecuritiesMember_019d8775-5d40-7ee2-b9f7-124ec656959f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CorporateDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019d8775-5d40-7b32-a43f-365b0fa23675" xlink:to="loc_us-gaap_CorporateDebtSecuritiesMember_019d8775-5d40-7ee2-b9f7-124ec656959f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesMember_019d8775-5d40-7a3c-a5b7-75a7e97205b9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019d8775-5d40-7b32-a43f-365b0fa23675" xlink:to="loc_us-gaap_DebtSecuritiesMember_019d8775-5d40-7a3c-a5b7-75a7e97205b9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesMember_019d8775-5d40-7a38-94d6-5b10e82908b6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquitySecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019d8775-5d40-7b32-a43f-365b0fa23675" xlink:to="loc_us-gaap_EquitySecuritiesMember_019d8775-5d40-7a38-94d6-5b10e82908b6" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_019d8775-5d40-77ee-b2c9-7c1ff9d34640" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_019d8775-5d40-76ef-a3d0-0ab769b656bb" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_019d8775-5d40-77ee-b2c9-7c1ff9d34640" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5d40-77ee-b2c9-7c1ff9d34640_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019d8775-5d40-77ee-b2c9-7c1ff9d34640" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5d40-77ee-b2c9-7c1ff9d34640_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5d40-78f6-8ea4-4bee2159cdcb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019d8775-5d40-77ee-b2c9-7c1ff9d34640" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5d40-78f6-8ea4-4bee2159cdcb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmbeddedDerivativeFinancialInstrumentsMember_019d8775-5d40-70a4-94a6-e3aba1ad93d9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmbeddedDerivativeFinancialInstrumentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5d40-78f6-8ea4-4bee2159cdcb" xlink:to="loc_us-gaap_EmbeddedDerivativeFinancialInstrumentsMember_019d8775-5d40-70a4-94a6-e3aba1ad93d9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019d8775-5d40-7bb6-bccb-0602624fab8a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019d8775-5d40-74ec-b514-062da6bbdd66" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019d8775-5d40-7bb6-bccb-0602624fab8a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue_019d8775-5d40-7854-9ae6-85b2b8a4c14a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019d8775-5d40-7bb6-bccb-0602624fab8a" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue_019d8775-5d40-7854-9ae6-85b2b8a4c14a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1_019d8775-5d40-7a18-87ad-72651307fc21" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019d8775-5d40-7bb6-bccb-0602624fab8a" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1_019d8775-5d40-7a18-87ad-72651307fc21" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss_019d8775-5d40-71be-be5b-34e99e753874" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019d8775-5d40-7bb6-bccb-0602624fab8a" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss_019d8775-5d40-71be-be5b-34e99e753874" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases_019d8775-5d40-72c1-808d-f35f3ec1c7d1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019d8775-5d40-7bb6-bccb-0602624fab8a" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases_019d8775-5d40-72c1-808d-f35f3ec1c7d1" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales_019d8775-5d40-7ed9-9a2c-6767121a271c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019d8775-5d40-7bb6-bccb-0602624fab8a" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales_019d8775-5d40-7ed9-9a2c-6767121a271c" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3_019d8775-5d40-7fbb-8441-d0deb0ccf068" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019d8775-5d40-7bb6-bccb-0602624fab8a" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3_019d8775-5d40-7fbb-8441-d0deb0ccf068" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3_019d8775-5d40-7907-ba99-546292ecc272" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019d8775-5d40-7bb6-bccb-0602624fab8a" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3_019d8775-5d40-7907-ba99-546292ecc272" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue_019d8775-5d40-7897-91ef-eed92e7de13e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetRecurringBasisStillHeldUnrealizedGainLossOci_019d8775-5d40-774a-9fd9-59ecd4d30d11" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetRecurringBasisStillHeldUnrealizedGainLossOci"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019d8775-5d40-7bb6-bccb-0602624fab8a" xlink:to="loc_us-gaap_FairValueAssetRecurringBasisStillHeldUnrealizedGainLossOci_019d8775-5d40-774a-9fd9-59ecd4d30d11" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisChangeInUnrealizedGainLoss_019d8775-5d40-7e26-b8ce-0da4c81f98fd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisChangeInUnrealizedGainLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019d8775-5d40-7bb6-bccb-0602624fab8a" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisChangeInUnrealizedGainLoss_019d8775-5d40-7e26-b8ce-0da4c81f98fd" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019d8775-5d40-7cf9-a565-248e1d5622d1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019d8775-5d40-74ec-b514-062da6bbdd66" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019d8775-5d40-7cf9-a565-248e1d5622d1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisWithUnobservableInputs_019d8775-5d40-7709-b1e6-0f723d37df4b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisWithUnobservableInputs"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019d8775-5d40-7cf9-a565-248e1d5622d1" xlink:to="loc_us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisWithUnobservableInputs_019d8775-5d40-7709-b1e6-0f723d37df4b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputsReconciliationGainLossIncludedInEarnings_019d8775-5d40-7b77-8c6d-3d736f4ef4ad" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputsReconciliationGainLossIncludedInEarnings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019d8775-5d40-7cf9-a565-248e1d5622d1" xlink:to="loc_us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputsReconciliationGainLossIncludedInEarnings_019d8775-5d40-7b77-8c6d-3d736f4ef4ad" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputsReconciliationGainLossIncludedInOtherComprehensiveIncomeLoss_019d8775-5d40-7239-815a-aff3787e359e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputsReconciliationGainLossIncludedInOtherComprehensiveIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019d8775-5d40-7cf9-a565-248e1d5622d1" xlink:to="loc_us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputsReconciliationGainLossIncludedInOtherComprehensiveIncomeLoss_019d8775-5d40-7239-815a-aff3787e359e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputsReconciliationPurchases_019d8775-5d40-7d5e-b11b-f75e97db5139" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputsReconciliationPurchases"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019d8775-5d40-7cf9-a565-248e1d5622d1" xlink:to="loc_us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputsReconciliationPurchases_019d8775-5d40-7d5e-b11b-f75e97db5139" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputsReconciliationSales_019d8775-5d40-7df2-a9db-357bc0a01290" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputsReconciliationSales"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019d8775-5d40-7cf9-a565-248e1d5622d1" xlink:to="loc_us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputsReconciliationSales_019d8775-5d40-7df2-a9db-357bc0a01290" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputsReconciliationTransfersIntoLevel3_019d8775-5d40-71ec-a976-cec14cf3e5fa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputsReconciliationTransfersIntoLevel3"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019d8775-5d40-7cf9-a565-248e1d5622d1" xlink:to="loc_us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputsReconciliationTransfersIntoLevel3_019d8775-5d40-71ec-a976-cec14cf3e5fa" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputsReconciliationTransfersOutOfLevel3_019d8775-5d40-7102-8806-bb4ae0dd9609" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputsReconciliationTransfersOutOfLevel3"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019d8775-5d40-7cf9-a565-248e1d5622d1" xlink:to="loc_us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputsReconciliationTransfersOutOfLevel3_019d8775-5d40-7102-8806-bb4ae0dd9609" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisWithUnobservableInputs_019d8775-5d40-7ed0-8c8c-da4c3a28e9d5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisWithUnobservableInputs"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueNetDerivativeAssetLiabilityRecurringBasisStillHeldUnrealizedGainLossOci_019d8775-5d40-7a87-9353-a8172425bad9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueNetDerivativeAssetLiabilityRecurringBasisStillHeldUnrealizedGainLossOci"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019d8775-5d40-7cf9-a565-248e1d5622d1" xlink:to="loc_us-gaap_FairValueNetDerivativeAssetLiabilityRecurringBasisStillHeldUnrealizedGainLossOci_019d8775-5d40-7a87-9353-a8172425bad9" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisChangeInUnrealizedGainLoss_019d8775-5d40-7b90-9889-c8f07f3c99ac" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisChangeInUnrealizedGainLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019d8775-5d40-7cf9-a565-248e1d5622d1" xlink:to="loc_us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisChangeInUnrealizedGainLoss_019d8775-5d40-7b90-9889-c8f07f3c99ac" xlink:type="arc" order="10"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.unum.com/role/QuantitativeInformationRegardingSignificantUnobservableInputsDetails" xlink:type="simple" xlink:href="unm-20260331.xsd#QuantitativeInformationRegardingSignificantUnobservableInputsDetails"/>
  <link:definitionLink xlink:role="http://www.unum.com/role/QuantitativeInformationRegardingSignificantUnobservableInputsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_019d8775-5d40-7f01-9d24-8874e928e876" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_019d8775-5d40-7bb4-8048-4a03d393a52b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_019d8775-5d40-7f01-9d24-8874e928e876" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_019d8775-5d40-7bb4-8048-4a03d393a52b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019d8775-5d40-7f49-ba93-cf718f5f84f1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_019d8775-5d40-7bb4-8048-4a03d393a52b" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019d8775-5d40-7f49-ba93-cf718f5f84f1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019d8775-5d40-7f49-ba93-cf718f5f84f1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019d8775-5d40-7f49-ba93-cf718f5f84f1" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019d8775-5d40-7f49-ba93-cf718f5f84f1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019d8775-5d40-745a-8bf2-8dffe42c7e0f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019d8775-5d40-7f49-ba93-cf718f5f84f1" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019d8775-5d40-745a-8bf2-8dffe42c7e0f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_019d8775-5d40-725e-a414-b72e3a501d7e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019d8775-5d40-745a-8bf2-8dffe42c7e0f" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_019d8775-5d40-725e-a414-b72e3a501d7e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_019d8775-5d40-7486-836c-06724fcb056c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_019d8775-5d40-7bb4-8048-4a03d393a52b" xlink:to="loc_us-gaap_FinancialInstrumentAxis_019d8775-5d40-7486-836c-06724fcb056c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5d40-7486-836c-06724fcb056c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019d8775-5d40-7486-836c-06724fcb056c" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5d40-7486-836c-06724fcb056c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5d40-7679-a869-eef2ba6711d9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019d8775-5d40-7486-836c-06724fcb056c" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5d40-7679-a869-eef2ba6711d9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateDebtSecuritiesMember_019d8775-5d40-72aa-bed5-f0878cc98870" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CorporateDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5d40-7679-a869-eef2ba6711d9" xlink:to="loc_us-gaap_CorporateDebtSecuritiesMember_019d8775-5d40-72aa-bed5-f0878cc98870" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesMember_019d8775-5d40-77a5-9824-76b6c85e3257" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquitySecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5d40-7679-a869-eef2ba6711d9" xlink:to="loc_us-gaap_EquitySecuritiesMember_019d8775-5d40-77a5-9824-76b6c85e3257" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueAxis_019d8775-5d40-7000-9aec-53388cba7f45" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ValuationTechniqueAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_019d8775-5d40-7bb4-8048-4a03d393a52b" xlink:to="loc_us-gaap_ValuationTechniqueAxis_019d8775-5d40-7000-9aec-53388cba7f45" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueDomain_019d8775-5d40-7000-9aec-53388cba7f45_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ValuationTechniqueDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ValuationTechniqueAxis_019d8775-5d40-7000-9aec-53388cba7f45" xlink:to="loc_us-gaap_ValuationTechniqueDomain_019d8775-5d40-7000-9aec-53388cba7f45_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueDomain_019d8775-5d40-7860-beb6-b3d9c5a50c36" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ValuationTechniqueDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ValuationTechniqueAxis_019d8775-5d40-7000-9aec-53388cba7f45" xlink:to="loc_us-gaap_ValuationTechniqueDomain_019d8775-5d40-7860-beb6-b3d9c5a50c36" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MarketApproachValuationTechniqueMember_019d8775-5d40-7740-acac-9d999600f223" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MarketApproachValuationTechniqueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ValuationTechniqueDomain_019d8775-5d40-7860-beb6-b3d9c5a50c36" xlink:to="loc_us-gaap_MarketApproachValuationTechniqueMember_019d8775-5d40-7740-acac-9d999600f223" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueDiscountedCashFlowMember_019d8775-5d40-761a-8102-cd11bff06846" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ValuationTechniqueDiscountedCashFlowMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ValuationTechniqueDomain_019d8775-5d40-7860-beb6-b3d9c5a50c36" xlink:to="loc_us-gaap_ValuationTechniqueDiscountedCashFlowMember_019d8775-5d40-761a-8102-cd11bff06846" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019d8775-5d40-786e-a964-1abaab6a33c4" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_019d8775-5d40-7bb4-8048-4a03d393a52b" xlink:to="loc_srt_RangeAxis_019d8775-5d40-786e-a964-1abaab6a33c4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019d8775-5d40-786e-a964-1abaab6a33c4_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019d8775-5d40-786e-a964-1abaab6a33c4" xlink:to="loc_srt_RangeMember_019d8775-5d40-786e-a964-1abaab6a33c4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019d8775-5d40-7e5a-9847-7f35092b2334" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019d8775-5d40-786e-a964-1abaab6a33c4" xlink:to="loc_srt_RangeMember_019d8775-5d40-7e5a-9847-7f35092b2334" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_WeightedAverageMember_019d8775-5d40-7f47-9b05-4935c4760fc5" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_WeightedAverageMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019d8775-5d40-7e5a-9847-7f35092b2334" xlink:to="loc_srt_WeightedAverageMember_019d8775-5d40-7f47-9b05-4935c4760fc5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeAxis_019d8775-5d40-74ca-8732-6f1de9e26959" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_019d8775-5d40-7bb4-8048-4a03d393a52b" xlink:to="loc_us-gaap_MeasurementInputTypeAxis_019d8775-5d40-74ca-8732-6f1de9e26959" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_019d8775-5d40-74ca-8732-6f1de9e26959_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_MeasurementInputTypeAxis_019d8775-5d40-74ca-8732-6f1de9e26959" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_019d8775-5d40-74ca-8732-6f1de9e26959_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_019d8775-5d40-7196-a37b-2d4be08fbbb4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_MeasurementInputTypeAxis_019d8775-5d40-74ca-8732-6f1de9e26959" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_019d8775-5d40-7196-a37b-2d4be08fbbb4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_InputMeasurementSpreadOfSwapCurveMember_019d8775-5d40-7ad8-9afa-127671a7b165" xlink:href="unm-20260331.xsd#unm_InputMeasurementSpreadOfSwapCurveMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_019d8775-5d40-7196-a37b-2d4be08fbbb4" xlink:to="loc_unm_InputMeasurementSpreadOfSwapCurveMember_019d8775-5d40-7ad8-9afa-127671a7b165" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_019d8775-5d40-770a-91d9-e9e154b8a656" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_019d8775-5d40-7bb4-8048-4a03d393a52b" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_019d8775-5d40-770a-91d9-e9e154b8a656" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5d40-770a-91d9-e9e154b8a656_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019d8775-5d40-770a-91d9-e9e154b8a656" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5d40-770a-91d9-e9e154b8a656_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5d40-7ed7-8c64-a5e6d6b2efa3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019d8775-5d40-770a-91d9-e9e154b8a656" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5d40-7ed7-8c64-a5e6d6b2efa3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmbeddedDerivativeFinancialInstrumentsMember_019d8775-5d40-73b3-92a4-716e0b4e5e09" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmbeddedDerivativeFinancialInstrumentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5d40-7ed7-8c64-a5e6d6b2efa3" xlink:to="loc_us-gaap_EmbeddedDerivativeFinancialInstrumentsMember_019d8775-5d40-73b3-92a4-716e0b4e5e09" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_019d8775-5d40-763b-b6b3-240525e9b0f6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_019d8775-5d40-7f01-9d24-8874e928e876" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_019d8775-5d40-763b-b6b3-240525e9b0f6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesFvNi_019d8775-5d40-7848-a5e8-1f9a946deda9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquitySecuritiesFvNi"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_019d8775-5d40-7f01-9d24-8874e928e876" xlink:to="loc_us-gaap_EquitySecuritiesFvNi_019d8775-5d40-7848-a5e8-1f9a946deda9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmbeddedDerivativeLiabilityMeasurementInput_019d8775-5d40-73c8-8f80-625c2ebb260b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmbeddedDerivativeLiabilityMeasurementInput"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_019d8775-5d40-7f01-9d24-8874e928e876" xlink:to="loc_us-gaap_EmbeddedDerivativeLiabilityMeasurementInput_019d8775-5d40-73c8-8f80-625c2ebb260b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmbeddedDerivativeFairValueOfEmbeddedDerivativeAsset_019d8775-5d40-72f5-9a3d-622d50f7a4bf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmbeddedDerivativeFairValueOfEmbeddedDerivativeAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_019d8775-5d40-7f01-9d24-8874e928e876" xlink:to="loc_us-gaap_EmbeddedDerivativeFairValueOfEmbeddedDerivativeAsset_019d8775-5d40-72f5-9a3d-622d50f7a4bf" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.unum.com/role/FairValuesofFinancialInstrumentsCarryingAmountsandEstimatedFairvalueofFinancialInstrumentsNotMeasuredatFairValueDetails" xlink:type="simple" xlink:href="unm-20260331.xsd#FairValuesofFinancialInstrumentsCarryingAmountsandEstimatedFairvalueofFinancialInstrumentsNotMeasuredatFairValueDetails"/>
  <link:definitionLink xlink:role="http://www.unum.com/role/FairValuesofFinancialInstrumentsCarryingAmountsandEstimatedFairvalueofFinancialInstrumentsNotMeasuredatFairValueDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_019d8775-5d40-73b1-bafb-370208ff8afa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByBalanceSheetGroupingTable_019d8775-5d40-7a29-bcef-b793286816fc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByBalanceSheetGroupingTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_019d8775-5d40-73b1-bafb-370208ff8afa" xlink:to="loc_us-gaap_FairValueByBalanceSheetGroupingTable_019d8775-5d40-7a29-bcef-b793286816fc" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019d8775-5d40-7e66-9450-582dc4bbd3bc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueByBalanceSheetGroupingTable_019d8775-5d40-7a29-bcef-b793286816fc" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019d8775-5d40-7e66-9450-582dc4bbd3bc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019d8775-5d40-7e66-9450-582dc4bbd3bc_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019d8775-5d40-7e66-9450-582dc4bbd3bc" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019d8775-5d40-7e66-9450-582dc4bbd3bc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019d8775-5d40-7ce1-85fd-8877845cc47c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019d8775-5d40-7e66-9450-582dc4bbd3bc" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019d8775-5d40-7ce1-85fd-8877845cc47c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_019d8775-5d40-7ff4-989c-1f71f6d56a38" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019d8775-5d40-7ce1-85fd-8877845cc47c" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_019d8775-5d40-7ff4-989c-1f71f6d56a38" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_019d8775-5d40-72af-92d8-9f86d89fe0ed" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019d8775-5d40-7ce1-85fd-8877845cc47c" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_019d8775-5d40-72af-92d8-9f86d89fe0ed" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_019d8775-5d40-7ce1-a827-5094a320de1d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019d8775-5d40-7ce1-85fd-8877845cc47c" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_019d8775-5d40-7ce1-a827-5094a320de1d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementFrequencyAxis_019d8775-5d40-72e2-957e-8a9aeae4349b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByMeasurementFrequencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueByBalanceSheetGroupingTable_019d8775-5d40-7a29-bcef-b793286816fc" xlink:to="loc_us-gaap_FairValueByMeasurementFrequencyAxis_019d8775-5d40-72e2-957e-8a9aeae4349b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_019d8775-5d40-72e2-957e-8a9aeae4349b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_019d8775-5d40-72e2-957e-8a9aeae4349b" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_019d8775-5d40-72e2-957e-8a9aeae4349b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_019d8775-5d40-7694-804d-a8f492f059f9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_019d8775-5d40-72e2-957e-8a9aeae4349b" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_019d8775-5d40-7694-804d-a8f492f059f9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsNonrecurringMember_019d8775-5d40-74f0-a58f-a90b1c643cbd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsNonrecurringMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementFrequencyDomain_019d8775-5d40-7694-804d-a8f492f059f9" xlink:to="loc_us-gaap_FairValueMeasurementsNonrecurringMember_019d8775-5d40-74f0-a58f-a90b1c643cbd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MortgagesHeldForSaleFairValueDisclosure_019d8775-5d40-7e0c-ac64-f38f680f31d8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MortgagesHeldForSaleFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_019d8775-5d40-73b1-bafb-370208ff8afa" xlink:to="loc_us-gaap_MortgagesHeldForSaleFairValueDisclosure_019d8775-5d40-7e0c-ac64-f38f680f31d8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MortgageLoansOnRealEstateCommercialAndConsumerNet_019d8775-5d40-79b1-9b4c-5e64a98fd94e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MortgageLoansOnRealEstateCommercialAndConsumerNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_019d8775-5d40-73b1-bafb-370208ff8afa" xlink:to="loc_us-gaap_MortgageLoansOnRealEstateCommercialAndConsumerNet_019d8775-5d40-79b1-9b4c-5e64a98fd94e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoansReceivableFairValueDisclosure_019d8775-5d40-771f-a273-156dce19c391" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LoansReceivableFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_019d8775-5d40-73b1-bafb-370208ff8afa" xlink:to="loc_us-gaap_LoansReceivableFairValueDisclosure_019d8775-5d40-771f-a273-156dce19c391" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoansInsurancePolicy_019d8775-5d40-70a9-8e3e-3833644eccee" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LoansInsurancePolicy"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_019d8775-5d40-73b1-bafb-370208ff8afa" xlink:to="loc_us-gaap_LoansInsurancePolicy_019d8775-5d40-70a9-8e3e-3833644eccee" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_MiscellaneousLongTermInvestments_019d8775-5d40-7f5b-bb62-f1daebe27dba" xlink:href="unm-20260331.xsd#unm_MiscellaneousLongTermInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_019d8775-5d40-73b1-bafb-370208ff8afa" xlink:to="loc_unm_MiscellaneousLongTermInvestments_019d8775-5d40-7f5b-bb62-f1daebe27dba" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_MiscellaneousLongTermInvestmentsCarryingValue_019d8775-5d40-7a9d-aa1a-533ae96d4d00" xlink:href="unm-20260331.xsd#unm_MiscellaneousLongTermInvestmentsCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_019d8775-5d40-73b1-bafb-370208ff8afa" xlink:to="loc_unm_MiscellaneousLongTermInvestmentsCarryingValue_019d8775-5d40-7a9d-aa1a-533ae96d4d00" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_FinancialInstrumentsFinancialAssetsFairValueDisclosureTotal_019d8775-5d40-7109-baa7-118354057b66" xlink:href="unm-20260331.xsd#unm_FinancialInstrumentsFinancialAssetsFairValueDisclosureTotal"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_019d8775-5d40-73b1-bafb-370208ff8afa" xlink:to="loc_unm_FinancialInstrumentsFinancialAssetsFairValueDisclosureTotal_019d8775-5d40-7109-baa7-118354057b66" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_FinancialInstrumentsFinancialAssetsFairValueDisclosureCarryingValue_019d8775-5d40-7538-b225-821b2f33955b" xlink:href="unm-20260331.xsd#unm_FinancialInstrumentsFinancialAssetsFairValueDisclosureCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_019d8775-5d40-73b1-bafb-370208ff8afa" xlink:to="loc_unm_FinancialInstrumentsFinancialAssetsFairValueDisclosureCarryingValue_019d8775-5d40-7538-b225-821b2f33955b" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesRelatedToInvestmentContractsFairValueDisclosure_019dbbf4-619e-7513-ac27-e5605ba55d42" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesRelatedToInvestmentContractsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_019d8775-5d40-73b1-bafb-370208ff8afa" xlink:to="loc_us-gaap_LiabilitiesRelatedToInvestmentContractsFairValueDisclosure_019dbbf4-619e-7513-ac27-e5605ba55d42" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NotesPayableFairValueDisclosure_019d8775-5d40-71cb-82b7-d3a0b59e9481" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NotesPayableFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_019d8775-5d40-73b1-bafb-370208ff8afa" xlink:to="loc_us-gaap_NotesPayableFairValueDisclosure_019d8775-5d40-71cb-82b7-d3a0b59e9481" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtAndCapitalLeaseObligations_019d8775-5d40-729a-9a7d-91468207290d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtAndCapitalLeaseObligations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_019d8775-5d40-73b1-bafb-370208ff8afa" xlink:to="loc_us-gaap_LongTermDebtAndCapitalLeaseObligations_019d8775-5d40-729a-9a7d-91468207290d" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_OtherLiabilitiesCarryingValue_019dbbf1-be3e-7fb1-9bff-b5edca76353b" xlink:href="unm-20260331.xsd#unm_OtherLiabilitiesCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_019d8775-5d40-73b1-bafb-370208ff8afa" xlink:to="loc_unm_OtherLiabilitiesCarryingValue_019dbbf1-be3e-7fb1-9bff-b5edca76353b" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilities_019dbbf1-4558-74ea-b145-3e2f583c3dc8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_019d8775-5d40-73b1-bafb-370208ff8afa" xlink:to="loc_us-gaap_OtherLiabilities_019dbbf1-4558-74ea-b145-3e2f583c3dc8" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesFairValueDisclosure_019d8775-5d40-7faa-9c5c-503d6e9b9a9f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_019d8775-5d40-73b1-bafb-370208ff8afa" xlink:to="loc_us-gaap_LiabilitiesFairValueDisclosure_019d8775-5d40-7faa-9c5c-503d6e9b9a9f" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_TotalFinancialInstrumentLiabilitiesNotCarriedatFairValue_019d8775-5d40-705d-aca1-3cc3c0403552" xlink:href="unm-20260331.xsd#unm_TotalFinancialInstrumentLiabilitiesNotCarriedatFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_019d8775-5d40-73b1-bafb-370208ff8afa" xlink:to="loc_unm_TotalFinancialInstrumentLiabilitiesNotCarriedatFairValue_019d8775-5d40-705d-aca1-3cc3c0403552" xlink:type="arc" order="14"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.unum.com/role/FairValueofFinancialInstrumentsAdditionalInformationDetail" xlink:type="simple" xlink:href="unm-20260331.xsd#FairValueofFinancialInstrumentsAdditionalInformationDetail"/>
  <link:definitionLink xlink:role="http://www.unum.com/role/FairValueofFinancialInstrumentsAdditionalInformationDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019d8775-5d40-786b-9171-34aa38c316da" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019d8775-5d40-72bb-87f4-ea5af8bafae3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019d8775-5d40-786b-9171-34aa38c316da" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019d8775-5d40-72bb-87f4-ea5af8bafae3" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_HeirarchyLevelCombinationAxis_019d8775-5d40-7df4-813b-27ae93793538" xlink:href="unm-20260331.xsd#unm_HeirarchyLevelCombinationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019d8775-5d40-72bb-87f4-ea5af8bafae3" xlink:to="loc_unm_HeirarchyLevelCombinationAxis_019d8775-5d40-7df4-813b-27ae93793538" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_HeirarchyLevelCombinationDomain_019d8775-5d40-7df4-813b-27ae93793538_default" xlink:href="unm-20260331.xsd#unm_HeirarchyLevelCombinationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_unm_HeirarchyLevelCombinationAxis_019d8775-5d40-7df4-813b-27ae93793538" xlink:to="loc_unm_HeirarchyLevelCombinationDomain_019d8775-5d40-7df4-813b-27ae93793538_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_HeirarchyLevelCombinationDomain_019d8775-5d40-7772-9df9-a129d5791e2c" xlink:href="unm-20260331.xsd#unm_HeirarchyLevelCombinationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_unm_HeirarchyLevelCombinationAxis_019d8775-5d40-7df4-813b-27ae93793538" xlink:to="loc_unm_HeirarchyLevelCombinationDomain_019d8775-5d40-7772-9df9-a129d5791e2c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_FairValueInputsOtherThanLevel1Member_019d8775-5d40-7516-9da3-978f9e314802" xlink:href="unm-20260331.xsd#unm_FairValueInputsOtherThanLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_unm_HeirarchyLevelCombinationDomain_019d8775-5d40-7772-9df9-a129d5791e2c" xlink:to="loc_unm_FairValueInputsOtherThanLevel1Member_019d8775-5d40-7516-9da3-978f9e314802" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_FairValueInputsLevel2OrLevel3Member_019d8775-5d40-76ce-ad11-24e5a3d58130" xlink:href="unm-20260331.xsd#unm_FairValueInputsLevel2OrLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_unm_HeirarchyLevelCombinationDomain_019d8775-5d40-7772-9df9-a129d5791e2c" xlink:to="loc_unm_FairValueInputsLevel2OrLevel3Member_019d8775-5d40-76ce-ad11-24e5a3d58130" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019d8775-5d40-7094-abf3-197a19699006" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019d8775-5d40-72bb-87f4-ea5af8bafae3" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019d8775-5d40-7094-abf3-197a19699006" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019d8775-5d40-7094-abf3-197a19699006_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019d8775-5d40-7094-abf3-197a19699006" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019d8775-5d40-7094-abf3-197a19699006_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019d8775-5d40-7d41-ab92-3e3c2d206b56" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019d8775-5d40-7094-abf3-197a19699006" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019d8775-5d40-7d41-ab92-3e3c2d206b56" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_019d8775-5d40-7669-b4a6-5a8f17868542" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019d8775-5d40-7d41-ab92-3e3c2d206b56" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_019d8775-5d40-7669-b4a6-5a8f17868542" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_019d8775-5d40-7d35-ac8a-9a5bbef016c9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019d8775-5d40-7d41-ab92-3e3c2d206b56" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_019d8775-5d40-7d35-ac8a-9a5bbef016c9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_FairValueAssetsAndLiabilitiesComponentsAxis_019d8775-5d40-779c-8cd8-00dfa0bc5876" xlink:href="unm-20260331.xsd#unm_FairValueAssetsAndLiabilitiesComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019d8775-5d40-72bb-87f4-ea5af8bafae3" xlink:to="loc_unm_FairValueAssetsAndLiabilitiesComponentsAxis_019d8775-5d40-779c-8cd8-00dfa0bc5876" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_FairValueAssetsandLiabilitiesComponentDomain_019d8775-5d40-779c-8cd8-00dfa0bc5876_default" xlink:href="unm-20260331.xsd#unm_FairValueAssetsandLiabilitiesComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_unm_FairValueAssetsAndLiabilitiesComponentsAxis_019d8775-5d40-779c-8cd8-00dfa0bc5876" xlink:to="loc_unm_FairValueAssetsandLiabilitiesComponentDomain_019d8775-5d40-779c-8cd8-00dfa0bc5876_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_FairValueAssetsandLiabilitiesComponentDomain_019d8775-5d40-77d0-aea4-65b83b8fe210" xlink:href="unm-20260331.xsd#unm_FairValueAssetsandLiabilitiesComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_unm_FairValueAssetsAndLiabilitiesComponentsAxis_019d8775-5d40-779c-8cd8-00dfa0bc5876" xlink:to="loc_unm_FairValueAssetsandLiabilitiesComponentDomain_019d8775-5d40-77d0-aea4-65b83b8fe210" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_PricingServiceMember_019d8775-5d40-7d13-9c87-250c9bb61ef7" xlink:href="unm-20260331.xsd#unm_PricingServiceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_unm_FairValueAssetsandLiabilitiesComponentDomain_019d8775-5d40-77d0-aea4-65b83b8fe210" xlink:to="loc_unm_PricingServiceMember_019d8775-5d40-7d13-9c87-250c9bb61ef7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_OtherObservableMarketDataMember_019d8775-5d40-711a-b08e-134c64a38d6f" xlink:href="unm-20260331.xsd#unm_OtherObservableMarketDataMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_unm_FairValueAssetsandLiabilitiesComponentDomain_019d8775-5d40-77d0-aea4-65b83b8fe210" xlink:to="loc_unm_OtherObservableMarketDataMember_019d8775-5d40-711a-b08e-134c64a38d6f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_AvailableForSaleSecuritiesPercentOfTotalFairValue_019d8775-5d40-7ccb-bfa9-5f76f9a0a6b2" xlink:href="unm-20260331.xsd#unm_AvailableForSaleSecuritiesPercentOfTotalFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019d8775-5d40-786b-9171-34aa38c316da" xlink:to="loc_unm_AvailableForSaleSecuritiesPercentOfTotalFairValue_019d8775-5d40-7ccb-bfa9-5f76f9a0a6b2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_PolicyLoansCededtoReinsurers_019d8775-5d40-79ce-815f-60ce4a55e00b" xlink:href="unm-20260331.xsd#unm_PolicyLoansCededtoReinsurers"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019d8775-5d40-786b-9171-34aa38c316da" xlink:to="loc_unm_PolicyLoansCededtoReinsurers_019d8775-5d40-79ce-815f-60ce4a55e00b" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.unum.com/role/AmortizedCostandFairValuesofSecuritiesbySecurityTypeDetail" xlink:type="simple" xlink:href="unm-20260331.xsd#AmortizedCostandFairValuesofSecuritiesbySecurityTypeDetail"/>
  <link:definitionLink xlink:role="http://www.unum.com/role/AmortizedCostandFairValuesofSecuritiesbySecurityTypeDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019d8775-5d40-7dae-be99-56573e30a2a1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_019d8775-5d40-720a-b3ef-6756fc04a62d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019d8775-5d40-7dae-be99-56573e30a2a1" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_019d8775-5d40-720a-b3ef-6756fc04a62d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_019d8775-5d40-761c-9687-52d78cfe1aa8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_019d8775-5d40-720a-b3ef-6756fc04a62d" xlink:to="loc_us-gaap_FinancialInstrumentAxis_019d8775-5d40-761c-9687-52d78cfe1aa8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5d40-761c-9687-52d78cfe1aa8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019d8775-5d40-761c-9687-52d78cfe1aa8" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5d40-761c-9687-52d78cfe1aa8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5d40-7fa2-9197-16585a358770" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019d8775-5d40-761c-9687-52d78cfe1aa8" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5d40-7fa2-9197-16585a358770" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USTreasuryAndGovernmentMember_019d8775-5d40-7a7c-aecb-af5fe16fa6c3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_USTreasuryAndGovernmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5d40-7fa2-9197-16585a358770" xlink:to="loc_us-gaap_USTreasuryAndGovernmentMember_019d8775-5d40-7a7c-aecb-af5fe16fa6c3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USStatesAndPoliticalSubdivisionsMember_019d8775-5d40-7d2e-bd3f-408895b7d87b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_USStatesAndPoliticalSubdivisionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5d40-7fa2-9197-16585a358770" xlink:to="loc_us-gaap_USStatesAndPoliticalSubdivisionsMember_019d8775-5d40-7d2e-bd3f-408895b7d87b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignGovernmentDebtSecuritiesMember_019d8775-5d40-7c19-8e74-e6f0094cd3a0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ForeignGovernmentDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5d40-7fa2-9197-16585a358770" xlink:to="loc_us-gaap_ForeignGovernmentDebtSecuritiesMember_019d8775-5d40-7c19-8e74-e6f0094cd3a0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PublicUtilityBondsMember_019d8775-5d40-7429-adaa-350b6360c65d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PublicUtilityBondsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5d40-7fa2-9197-16585a358770" xlink:to="loc_us-gaap_PublicUtilityBondsMember_019d8775-5d40-7429-adaa-350b6360c65d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetBackedSecuritiesMember_019d8775-5d40-7155-80f9-87c1c24d46fd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetBackedSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5d40-7fa2-9197-16585a358770" xlink:to="loc_us-gaap_AssetBackedSecuritiesMember_019d8775-5d40-7155-80f9-87c1c24d46fd" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllOtherCorporateBondsMember_019d8775-5d40-728d-a945-01f6c8478db0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllOtherCorporateBondsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5d40-7fa2-9197-16585a358770" xlink:to="loc_us-gaap_AllOtherCorporateBondsMember_019d8775-5d40-728d-a945-01f6c8478db0" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RedeemablePreferredStockMember_019d8775-5d40-74ea-bcce-4098435ba059" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RedeemablePreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5d40-7fa2-9197-16585a358770" xlink:to="loc_us-gaap_RedeemablePreferredStockMember_019d8775-5d40-74ea-bcce-4098435ba059" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesMember_019d8775-5d40-7bd4-b7ea-f0ad642cbfdc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5d40-7fa2-9197-16585a358770" xlink:to="loc_us-gaap_DebtSecuritiesMember_019d8775-5d40-7bd4-b7ea-f0ad642cbfdc" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_019d8775-5d40-7079-86b8-adad57a9320c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019d8775-5d40-7dae-be99-56573e30a2a1" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_019d8775-5d40-7079-86b8-adad57a9320c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLoss_019d8775-5d40-7f44-8dc4-a6349b8d7362" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019d8775-5d40-7dae-be99-56573e30a2a1" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLoss_019d8775-5d40-7f44-8dc4-a6349b8d7362" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_019d8775-5d40-7c60-9658-3fbdadf5240c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019d8775-5d40-7dae-be99-56573e30a2a1" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_019d8775-5d40-7c60-9658-3fbdadf5240c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_019d8775-5d40-7ae1-a6fa-b6b8b6193fd1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019d8775-5d40-7dae-be99-56573e30a2a1" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_019d8775-5d40-7ae1-a6fa-b6b8b6193fd1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_019d8775-5d40-7ca0-9555-78df998ecbbd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019d8775-5d40-7dae-be99-56573e30a2a1" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_019d8775-5d40-7ca0-9555-78df998ecbbd" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.unum.com/role/LengthofTimeFixedMaturitySecuritieshadbeeninaGrossUnrealizedLossPositionDetail" xlink:type="simple" xlink:href="unm-20260331.xsd#LengthofTimeFixedMaturitySecuritieshadbeeninaGrossUnrealizedLossPositionDetail"/>
  <link:definitionLink xlink:role="http://www.unum.com/role/LengthofTimeFixedMaturitySecuritieshadbeeninaGrossUnrealizedLossPositionDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValueAbstract_019d8775-5d40-7714-b3bd-8080af5002ab" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValueAbstract"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionFairValueTable_019d8775-5d40-724e-9a6a-f2f35a0aeca4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionFairValueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValueAbstract_019d8775-5d40-7714-b3bd-8080af5002ab" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionFairValueTable_019d8775-5d40-724e-9a6a-f2f35a0aeca4" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_019d8775-5d40-71ff-b510-615e524f644d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionFairValueTable_019d8775-5d40-724e-9a6a-f2f35a0aeca4" xlink:to="loc_us-gaap_FinancialInstrumentAxis_019d8775-5d40-71ff-b510-615e524f644d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5d40-71ff-b510-615e524f644d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019d8775-5d40-71ff-b510-615e524f644d" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5d40-71ff-b510-615e524f644d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5d40-76b1-b751-3d435f23ad39" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019d8775-5d40-71ff-b510-615e524f644d" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5d40-76b1-b751-3d435f23ad39" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USTreasuryAndGovernmentMember_019d8775-5d40-7ce3-9952-5dc72804318b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_USTreasuryAndGovernmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5d40-76b1-b751-3d435f23ad39" xlink:to="loc_us-gaap_USTreasuryAndGovernmentMember_019d8775-5d40-7ce3-9952-5dc72804318b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USStatesAndPoliticalSubdivisionsMember_019d8775-5d40-77e3-8d7c-22fad77841cf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_USStatesAndPoliticalSubdivisionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5d40-76b1-b751-3d435f23ad39" xlink:to="loc_us-gaap_USStatesAndPoliticalSubdivisionsMember_019d8775-5d40-77e3-8d7c-22fad77841cf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignGovernmentDebtSecuritiesMember_019d8775-5d40-71e2-b324-19ca169613c5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ForeignGovernmentDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5d40-76b1-b751-3d435f23ad39" xlink:to="loc_us-gaap_ForeignGovernmentDebtSecuritiesMember_019d8775-5d40-71e2-b324-19ca169613c5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PublicUtilityBondsMember_019d8775-5d40-7314-8086-cab87a5820e0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PublicUtilityBondsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5d40-76b1-b751-3d435f23ad39" xlink:to="loc_us-gaap_PublicUtilityBondsMember_019d8775-5d40-7314-8086-cab87a5820e0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetBackedSecuritiesMember_019d8775-5d40-7da2-9154-8c5b0dd94b1b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetBackedSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5d40-76b1-b751-3d435f23ad39" xlink:to="loc_us-gaap_AssetBackedSecuritiesMember_019d8775-5d40-7da2-9154-8c5b0dd94b1b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllOtherCorporateBondsMember_019d8775-5d40-71bb-90ab-39aea427fc7e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllOtherCorporateBondsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5d40-76b1-b751-3d435f23ad39" xlink:to="loc_us-gaap_AllOtherCorporateBondsMember_019d8775-5d40-71bb-90ab-39aea427fc7e" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RedeemablePreferredStockMember_019d8775-5d40-79c5-a36d-6dced2e9ea45" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RedeemablePreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5d40-76b1-b751-3d435f23ad39" xlink:to="loc_us-gaap_RedeemablePreferredStockMember_019d8775-5d40-79c5-a36d-6dced2e9ea45" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months_019d8775-5d40-7098-a801-a18c03bd5eed" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValueAbstract_019d8775-5d40-7714-b3bd-8080af5002ab" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months_019d8775-5d40-7098-a801-a18c03bd5eed" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss_019d8775-5d40-762b-a954-9b506c4007eb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValueAbstract_019d8775-5d40-7714-b3bd-8080af5002ab" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss_019d8775-5d40-762b-a954-9b506c4007eb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger_019d8775-5d40-7a06-97b9-2bcfb69b7287" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValueAbstract_019d8775-5d40-7714-b3bd-8080af5002ab" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger_019d8775-5d40-7a06-97b9-2bcfb69b7287" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss_019d8775-5d40-766d-87d2-834d0cb38e38" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValueAbstract_019d8775-5d40-7714-b3bd-8080af5002ab" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss_019d8775-5d40-766d-87d2-834d0cb38e38" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.unum.com/role/InvestmentsDistributionoftheMaturityDatesforFixedMaturitySecuritiesDetails" xlink:type="simple" xlink:href="unm-20260331.xsd#InvestmentsDistributionoftheMaturityDatesforFixedMaturitySecuritiesDetails"/>
  <link:definitionLink xlink:role="http://www.unum.com/role/InvestmentsDistributionoftheMaturityDatesforFixedMaturitySecuritiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019d8775-5d40-7f3b-9d64-002451bac411" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_019d8775-5d40-7cbd-b11f-2cf1b04b2ba1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019d8775-5d40-7f3b-9d64-002451bac411" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_019d8775-5d40-7cbd-b11f-2cf1b04b2ba1" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_DebtSecuritiesAvailableforsaleUnrealizedGainLossFairValueAxis_019d8775-5d40-7be4-9510-cdbc48823501" xlink:href="unm-20260331.xsd#unm_DebtSecuritiesAvailableforsaleUnrealizedGainLossFairValueAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_019d8775-5d40-7cbd-b11f-2cf1b04b2ba1" xlink:to="loc_unm_DebtSecuritiesAvailableforsaleUnrealizedGainLossFairValueAxis_019d8775-5d40-7be4-9510-cdbc48823501" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_DebtSecuritiesAvailableforsaleUnrealizedGainLossFairValueDomain_019d8775-5d40-7be4-9510-cdbc48823501_default" xlink:href="unm-20260331.xsd#unm_DebtSecuritiesAvailableforsaleUnrealizedGainLossFairValueDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_unm_DebtSecuritiesAvailableforsaleUnrealizedGainLossFairValueAxis_019d8775-5d40-7be4-9510-cdbc48823501" xlink:to="loc_unm_DebtSecuritiesAvailableforsaleUnrealizedGainLossFairValueDomain_019d8775-5d40-7be4-9510-cdbc48823501_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_DebtSecuritiesAvailableforsaleUnrealizedGainLossFairValueDomain_019d8775-5d40-7d68-a79f-f544ae960947" xlink:href="unm-20260331.xsd#unm_DebtSecuritiesAvailableforsaleUnrealizedGainLossFairValueDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_unm_DebtSecuritiesAvailableforsaleUnrealizedGainLossFairValueAxis_019d8775-5d40-7be4-9510-cdbc48823501" xlink:to="loc_unm_DebtSecuritiesAvailableforsaleUnrealizedGainLossFairValueDomain_019d8775-5d40-7d68-a79f-f544ae960947" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_AvailableForSaleSecuritiesUnrealizedGainPositionFairValueMember_019d8775-5d40-7f91-9789-9f999206b892" xlink:href="unm-20260331.xsd#unm_AvailableForSaleSecuritiesUnrealizedGainPositionFairValueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_unm_DebtSecuritiesAvailableforsaleUnrealizedGainLossFairValueDomain_019d8775-5d40-7d68-a79f-f544ae960947" xlink:to="loc_unm_AvailableForSaleSecuritiesUnrealizedGainPositionFairValueMember_019d8775-5d40-7f91-9789-9f999206b892" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_AvailableForSaleSecuritiesUnrealizedLossPositionFairValueMember_019d8775-5d40-7e2e-98a9-f745356f1591" xlink:href="unm-20260331.xsd#unm_AvailableForSaleSecuritiesUnrealizedLossPositionFairValueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_unm_DebtSecuritiesAvailableforsaleUnrealizedGainLossFairValueDomain_019d8775-5d40-7d68-a79f-f544ae960947" xlink:to="loc_unm_AvailableForSaleSecuritiesUnrealizedLossPositionFairValueMember_019d8775-5d40-7e2e-98a9-f745356f1591" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_DebtSecuritiesAvailableForSaleAmortizedCostNetOfAllowanceForCreditLossesFiscalYearMaturityAbstract_019d8775-5d40-788b-9679-ee968f342ef9" xlink:href="unm-20260331.xsd#unm_DebtSecuritiesAvailableForSaleAmortizedCostNetOfAllowanceForCreditLossesFiscalYearMaturityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019d8775-5d40-7f3b-9d64-002451bac411" xlink:to="loc_unm_DebtSecuritiesAvailableForSaleAmortizedCostNetOfAllowanceForCreditLossesFiscalYearMaturityAbstract_019d8775-5d40-788b-9679-ee968f342ef9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_DebtSecuritiesAvailableForSaleAmortizedCostMaturityAllocatedAndSingleMaturityDateYearOneNet_019d8775-5d40-7620-948c-5b8e00aee6c4" xlink:href="unm-20260331.xsd#unm_DebtSecuritiesAvailableForSaleAmortizedCostMaturityAllocatedAndSingleMaturityDateYearOneNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_unm_DebtSecuritiesAvailableForSaleAmortizedCostNetOfAllowanceForCreditLossesFiscalYearMaturityAbstract_019d8775-5d40-788b-9679-ee968f342ef9" xlink:to="loc_unm_DebtSecuritiesAvailableForSaleAmortizedCostMaturityAllocatedAndSingleMaturityDateYearOneNet_019d8775-5d40-7620-948c-5b8e00aee6c4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_DebtSecuritiesAvailableForSaleAmortizedCostMaturityAllocatedAndSingleMaturityDateAfterYearOneThroughFiveNet_019d8775-5d40-7739-9af4-3d93694f9b5c" xlink:href="unm-20260331.xsd#unm_DebtSecuritiesAvailableForSaleAmortizedCostMaturityAllocatedAndSingleMaturityDateAfterYearOneThroughFiveNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_unm_DebtSecuritiesAvailableForSaleAmortizedCostNetOfAllowanceForCreditLossesFiscalYearMaturityAbstract_019d8775-5d40-788b-9679-ee968f342ef9" xlink:to="loc_unm_DebtSecuritiesAvailableForSaleAmortizedCostMaturityAllocatedAndSingleMaturityDateAfterYearOneThroughFiveNet_019d8775-5d40-7739-9af4-3d93694f9b5c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_DebtSecuritiesAvailableForSaleAmortizedCostMaturityAllocatedAndSingleMaturityDateAfterYear5Through10Net_019d8775-5d40-7980-ba78-fd282f5fa3a2" xlink:href="unm-20260331.xsd#unm_DebtSecuritiesAvailableForSaleAmortizedCostMaturityAllocatedAndSingleMaturityDateAfterYear5Through10Net"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_unm_DebtSecuritiesAvailableForSaleAmortizedCostNetOfAllowanceForCreditLossesFiscalYearMaturityAbstract_019d8775-5d40-788b-9679-ee968f342ef9" xlink:to="loc_unm_DebtSecuritiesAvailableForSaleAmortizedCostMaturityAllocatedAndSingleMaturityDateAfterYear5Through10Net_019d8775-5d40-7980-ba78-fd282f5fa3a2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_DebtSecuritiesAvailableForSaleAmortizedCostMaturityAllocatedAndSingleMaturityDateAfterYear10Net_019d8775-5d40-78cf-9bf3-b86cc1a28fcd" xlink:href="unm-20260331.xsd#unm_DebtSecuritiesAvailableForSaleAmortizedCostMaturityAllocatedAndSingleMaturityDateAfterYear10Net"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_unm_DebtSecuritiesAvailableForSaleAmortizedCostNetOfAllowanceForCreditLossesFiscalYearMaturityAbstract_019d8775-5d40-788b-9679-ee968f342ef9" xlink:to="loc_unm_DebtSecuritiesAvailableForSaleAmortizedCostMaturityAllocatedAndSingleMaturityDateAfterYear10Net_019d8775-5d40-78cf-9bf3-b86cc1a28fcd" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_AvailableForSaleSecuritiesDebtMaturitiesAmortizedCostGrossSubtotalNet_019d8775-5d40-7330-acc7-cd5126b25b56" xlink:href="unm-20260331.xsd#unm_AvailableForSaleSecuritiesDebtMaturitiesAmortizedCostGrossSubtotalNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_unm_DebtSecuritiesAvailableForSaleAmortizedCostNetOfAllowanceForCreditLossesFiscalYearMaturityAbstract_019d8775-5d40-788b-9679-ee968f342ef9" xlink:to="loc_unm_AvailableForSaleSecuritiesDebtMaturitiesAmortizedCostGrossSubtotalNet_019d8775-5d40-7330-acc7-cd5126b25b56" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_DebtSecuritiesAvailableForSaleMaturityWithoutSingleMaturityDateAmortizedCostNet_019d8775-5d40-7fcf-b5d7-b3bd8b33e333" xlink:href="unm-20260331.xsd#unm_DebtSecuritiesAvailableForSaleMaturityWithoutSingleMaturityDateAmortizedCostNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_unm_DebtSecuritiesAvailableForSaleAmortizedCostNetOfAllowanceForCreditLossesFiscalYearMaturityAbstract_019d8775-5d40-788b-9679-ee968f342ef9" xlink:to="loc_unm_DebtSecuritiesAvailableForSaleMaturityWithoutSingleMaturityDateAmortizedCostNet_019d8775-5d40-7fcf-b5d7-b3bd8b33e333" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_DebtSecuritiesAvailableForSaleAmortizedCostNetOfAllowanceForCreditLosses_019d8775-5d40-73e5-83ef-9e9de9fada95" xlink:href="unm-20260331.xsd#unm_DebtSecuritiesAvailableForSaleAmortizedCostNetOfAllowanceForCreditLosses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_unm_DebtSecuritiesAvailableForSaleAmortizedCostNetOfAllowanceForCreditLossesFiscalYearMaturityAbstract_019d8775-5d40-788b-9679-ee968f342ef9" xlink:to="loc_unm_DebtSecuritiesAvailableForSaleAmortizedCostNetOfAllowanceForCreditLosses_019d8775-5d40-73e5-83ef-9e9de9fada95" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_AvailableForSaleSecuritiesUnrealizedGainPositionGrossGain_019d8775-5d40-7b70-92f2-18c110a15ec4" xlink:href="unm-20260331.xsd#unm_AvailableForSaleSecuritiesUnrealizedGainPositionGrossGain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019d8775-5d40-7f3b-9d64-002451bac411" xlink:to="loc_unm_AvailableForSaleSecuritiesUnrealizedGainPositionGrossGain_019d8775-5d40-7b70-92f2-18c110a15ec4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearUnrealizedGainPositionGrossGain_019d8775-5d40-7ecf-b416-7bcd1c0fd675" xlink:href="unm-20260331.xsd#unm_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearUnrealizedGainPositionGrossGain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_unm_AvailableForSaleSecuritiesUnrealizedGainPositionGrossGain_019d8775-5d40-7b70-92f2-18c110a15ec4" xlink:to="loc_unm_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearUnrealizedGainPositionGrossGain_019d8775-5d40-7ecf-b416-7bcd1c0fd675" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsUnrealizedGainPositionGrossGain_019d8775-5d40-7cac-8004-edca9a3fe883" xlink:href="unm-20260331.xsd#unm_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsUnrealizedGainPositionGrossGain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_unm_AvailableForSaleSecuritiesUnrealizedGainPositionGrossGain_019d8775-5d40-7b70-92f2-18c110a15ec4" xlink:to="loc_unm_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsUnrealizedGainPositionGrossGain_019d8775-5d40-7cac-8004-edca9a3fe883" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsUnrealizedGainPositionGrossGain_019d8775-5d40-7d1b-b444-c6f8a67c15cd" xlink:href="unm-20260331.xsd#unm_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsUnrealizedGainPositionGrossGain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_unm_AvailableForSaleSecuritiesUnrealizedGainPositionGrossGain_019d8775-5d40-7b70-92f2-18c110a15ec4" xlink:to="loc_unm_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsUnrealizedGainPositionGrossGain_019d8775-5d40-7d1b-b444-c6f8a67c15cd" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsUnrealizedGainPositionGrossGain_019d8775-5d40-7903-9768-61782610f605" xlink:href="unm-20260331.xsd#unm_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsUnrealizedGainPositionGrossGain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_unm_AvailableForSaleSecuritiesUnrealizedGainPositionGrossGain_019d8775-5d40-7b70-92f2-18c110a15ec4" xlink:to="loc_unm_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsUnrealizedGainPositionGrossGain_019d8775-5d40-7903-9768-61782610f605" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_AvailableForSaleSecuritiesDebtMaturitiesUnrealizedGainPositionGrossGainGrossSubtotal_019d8775-5d40-73e6-980b-803140d5980c" xlink:href="unm-20260331.xsd#unm_AvailableForSaleSecuritiesDebtMaturitiesUnrealizedGainPositionGrossGainGrossSubtotal"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_unm_AvailableForSaleSecuritiesUnrealizedGainPositionGrossGain_019d8775-5d40-7b70-92f2-18c110a15ec4" xlink:to="loc_unm_AvailableForSaleSecuritiesDebtMaturitiesUnrealizedGainPositionGrossGainGrossSubtotal_019d8775-5d40-73e6-980b-803140d5980c" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateUnrealizedGainPositionGrossGain_019d8775-5d40-7fe1-9b0f-c524ccf8817a" xlink:href="unm-20260331.xsd#unm_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateUnrealizedGainPositionGrossGain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_unm_AvailableForSaleSecuritiesUnrealizedGainPositionGrossGain_019d8775-5d40-7b70-92f2-18c110a15ec4" xlink:to="loc_unm_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateUnrealizedGainPositionGrossGain_019d8775-5d40-7fe1-9b0f-c524ccf8817a" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_AvailableforsaleSecuritiesDebtMaturitiesUnrealizedGainPositionGrossGain_019d8775-5d40-7d65-93ef-aa5d546d086b" xlink:href="unm-20260331.xsd#unm_AvailableforsaleSecuritiesDebtMaturitiesUnrealizedGainPositionGrossGain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_unm_AvailableForSaleSecuritiesUnrealizedGainPositionGrossGain_019d8775-5d40-7b70-92f2-18c110a15ec4" xlink:to="loc_unm_AvailableforsaleSecuritiesDebtMaturitiesUnrealizedGainPositionGrossGain_019d8775-5d40-7d65-93ef-aa5d546d086b" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_AvailableForSaleSecuritiesUnrealizedLossPositionGrossLoss_019d8775-5d40-7f88-9cf7-ee379997e624" xlink:href="unm-20260331.xsd#unm_AvailableForSaleSecuritiesUnrealizedLossPositionGrossLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019d8775-5d40-7f3b-9d64-002451bac411" xlink:to="loc_unm_AvailableForSaleSecuritiesUnrealizedLossPositionGrossLoss_019d8775-5d40-7f88-9cf7-ee379997e624" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearUnrealizedLossPositionGrossLoss_019d8775-5d40-7518-ac77-865914affe62" xlink:href="unm-20260331.xsd#unm_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearUnrealizedLossPositionGrossLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_unm_AvailableForSaleSecuritiesUnrealizedLossPositionGrossLoss_019d8775-5d40-7f88-9cf7-ee379997e624" xlink:to="loc_unm_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearUnrealizedLossPositionGrossLoss_019d8775-5d40-7518-ac77-865914affe62" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsUnrealizedLossPositionGrossLoss_019d8775-5d40-7bce-94f6-4938592e9630" xlink:href="unm-20260331.xsd#unm_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsUnrealizedLossPositionGrossLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_unm_AvailableForSaleSecuritiesUnrealizedLossPositionGrossLoss_019d8775-5d40-7f88-9cf7-ee379997e624" xlink:to="loc_unm_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsUnrealizedLossPositionGrossLoss_019d8775-5d40-7bce-94f6-4938592e9630" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsUnrealizedLossPositionGrossLoss_019d8775-5d40-7326-86ed-d7572c5ff58d" xlink:href="unm-20260331.xsd#unm_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsUnrealizedLossPositionGrossLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_unm_AvailableForSaleSecuritiesUnrealizedLossPositionGrossLoss_019d8775-5d40-7f88-9cf7-ee379997e624" xlink:to="loc_unm_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsUnrealizedLossPositionGrossLoss_019d8775-5d40-7326-86ed-d7572c5ff58d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsUnrealizedLossPositionGrossLoss_019d8775-5d40-7e90-9f71-d3c4f8229d7b" xlink:href="unm-20260331.xsd#unm_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsUnrealizedLossPositionGrossLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_unm_AvailableForSaleSecuritiesUnrealizedLossPositionGrossLoss_019d8775-5d40-7f88-9cf7-ee379997e624" xlink:to="loc_unm_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsUnrealizedLossPositionGrossLoss_019d8775-5d40-7e90-9f71-d3c4f8229d7b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_AvailableForSaleSecuritiesDebtMaturitiesUnrealizedGainPositionGrossLossGrossSubtotal_019d8775-5d40-7591-88f5-a90aebd7a403" xlink:href="unm-20260331.xsd#unm_AvailableForSaleSecuritiesDebtMaturitiesUnrealizedGainPositionGrossLossGrossSubtotal"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_unm_AvailableForSaleSecuritiesUnrealizedLossPositionGrossLoss_019d8775-5d40-7f88-9cf7-ee379997e624" xlink:to="loc_unm_AvailableForSaleSecuritiesDebtMaturitiesUnrealizedGainPositionGrossLossGrossSubtotal_019d8775-5d40-7591-88f5-a90aebd7a403" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateUnrealizedLossPositionGrossLoss_019d8775-5d40-7913-9baf-602eaf7e5f97" xlink:href="unm-20260331.xsd#unm_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateUnrealizedLossPositionGrossLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_unm_AvailableForSaleSecuritiesUnrealizedLossPositionGrossLoss_019d8775-5d40-7f88-9cf7-ee379997e624" xlink:to="loc_unm_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateUnrealizedLossPositionGrossLoss_019d8775-5d40-7913-9baf-602eaf7e5f97" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_AvailableForSaleSecuritiesUnrealizedLossPositionGrossLossSubtotal_019d8775-5d40-7a3f-abc3-a355d1e434fa" xlink:href="unm-20260331.xsd#unm_AvailableForSaleSecuritiesUnrealizedLossPositionGrossLossSubtotal"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_unm_AvailableForSaleSecuritiesUnrealizedLossPositionGrossLoss_019d8775-5d40-7f88-9cf7-ee379997e624" xlink:to="loc_unm_AvailableForSaleSecuritiesUnrealizedLossPositionGrossLossSubtotal_019d8775-5d40-7a3f-abc3-a355d1e434fa" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_FairValueMaturityDistributionAbstract_019d8775-5d40-7183-a1e6-045aa89649bd" xlink:href="unm-20260331.xsd#unm_FairValueMaturityDistributionAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019d8775-5d40-7f3b-9d64-002451bac411" xlink:to="loc_unm_FairValueMaturityDistributionAbstract_019d8775-5d40-7183-a1e6-045aa89649bd" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue_019d8775-5d40-7494-aa54-0abc375f57ba" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_unm_FairValueMaturityDistributionAbstract_019d8775-5d40-7183-a1e6-045aa89649bd" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue_019d8775-5d40-7494-aa54-0abc375f57ba" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue_019d8775-5d40-74b6-a073-3b8d771d5a5e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_unm_FairValueMaturityDistributionAbstract_019d8775-5d40-7183-a1e6-045aa89649bd" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue_019d8775-5d40-74b6-a073-3b8d771d5a5e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue_019d8775-5d40-761c-aa0a-b8bc88dfa4a5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_unm_FairValueMaturityDistributionAbstract_019d8775-5d40-7183-a1e6-045aa89649bd" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue_019d8775-5d40-761c-aa0a-b8bc88dfa4a5" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsFairValue_019d8775-5d40-7e8b-a93e-abe989025ec4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_unm_FairValueMaturityDistributionAbstract_019d8775-5d40-7183-a1e6-045aa89649bd" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsFairValue_019d8775-5d40-7e8b-a93e-abe989025ec4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_AvailableForSaleSecuritiesDebtMaturitiesFairValueGrossSubtotal_019d8775-5d40-7edc-9c48-17245c33d96b" xlink:href="unm-20260331.xsd#unm_AvailableForSaleSecuritiesDebtMaturitiesFairValueGrossSubtotal"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_unm_FairValueMaturityDistributionAbstract_019d8775-5d40-7183-a1e6-045aa89649bd" xlink:to="loc_unm_AvailableForSaleSecuritiesDebtMaturitiesFairValueGrossSubtotal_019d8775-5d40-7edc-9c48-17245c33d96b" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateFairValue_019d8775-5d40-7841-a73a-b3a02e00ef65" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_unm_FairValueMaturityDistributionAbstract_019d8775-5d40-7183-a1e6-045aa89649bd" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateFairValue_019d8775-5d40-7841-a73a-b3a02e00ef65" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_019d8775-5d40-77a3-a951-8b749f879ca7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_unm_FairValueMaturityDistributionAbstract_019d8775-5d40-7183-a1e6-045aa89649bd" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_019d8775-5d40-77a3-a951-8b749f879ca7" xlink:type="arc" order="7"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.unum.com/role/InvestmentsDistributionbyExternalCreditRatingforFixedMaturitySecuritiesDetails" xlink:type="simple" xlink:href="unm-20260331.xsd#InvestmentsDistributionbyExternalCreditRatingforFixedMaturitySecuritiesDetails"/>
  <link:definitionLink xlink:role="http://www.unum.com/role/InvestmentsDistributionbyExternalCreditRatingforFixedMaturitySecuritiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019d8775-5d40-78d6-8683-7581a8592b00" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfGuaranteeObligationsTable_019d8775-5d40-7560-80b1-e82d6accee58" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfGuaranteeObligationsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019d8775-5d40-78d6-8683-7581a8592b00" xlink:to="loc_us-gaap_ScheduleOfGuaranteeObligationsTable_019d8775-5d40-7560-80b1-e82d6accee58" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ExternalCreditRatingByGroupingAxis_019d8775-5d40-7210-abf8-c043f51a5c7b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ExternalCreditRatingByGroupingAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfGuaranteeObligationsTable_019d8775-5d40-7560-80b1-e82d6accee58" xlink:to="loc_us-gaap_ExternalCreditRatingByGroupingAxis_019d8775-5d40-7210-abf8-c043f51a5c7b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ExternalCreditRatingByGroupingDomain_019d8775-5d40-7210-abf8-c043f51a5c7b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ExternalCreditRatingByGroupingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ExternalCreditRatingByGroupingAxis_019d8775-5d40-7210-abf8-c043f51a5c7b" xlink:to="loc_us-gaap_ExternalCreditRatingByGroupingDomain_019d8775-5d40-7210-abf8-c043f51a5c7b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ExternalCreditRatingByGroupingDomain_019d8775-5d40-764c-bb81-11f6808753cd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ExternalCreditRatingByGroupingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ExternalCreditRatingByGroupingAxis_019d8775-5d40-7210-abf8-c043f51a5c7b" xlink:to="loc_us-gaap_ExternalCreditRatingByGroupingDomain_019d8775-5d40-764c-bb81-11f6808753cd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ExternalCreditRatingInvestmentGradeMember_019d8775-5d40-76f9-8a12-61c1651bf00c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ExternalCreditRatingInvestmentGradeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ExternalCreditRatingByGroupingDomain_019d8775-5d40-764c-bb81-11f6808753cd" xlink:to="loc_us-gaap_ExternalCreditRatingInvestmentGradeMember_019d8775-5d40-76f9-8a12-61c1651bf00c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ExternalCreditRatingNonInvestmentGradeMember_019d8775-5d40-7688-b18b-de78f4eecd65" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ExternalCreditRatingNonInvestmentGradeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ExternalCreditRatingByGroupingDomain_019d8775-5d40-764c-bb81-11f6808753cd" xlink:to="loc_us-gaap_ExternalCreditRatingNonInvestmentGradeMember_019d8775-5d40-7688-b18b-de78f4eecd65" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_019d8775-5d40-7c55-80b1-fac74cf93d11" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019d8775-5d40-78d6-8683-7581a8592b00" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_019d8775-5d40-7c55-80b1-fac74cf93d11" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_019d8775-5d40-7cd7-8fcd-8dc40a2dfc2f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019d8775-5d40-78d6-8683-7581a8592b00" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_019d8775-5d40-7cd7-8fcd-8dc40a2dfc2f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_019d8775-5d40-77d1-a6ac-3e2b679f9efb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019d8775-5d40-78d6-8683-7581a8592b00" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_019d8775-5d40-77d1-a6ac-3e2b679f9efb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_FixedMaturitySecuritiesInUnrealizedLossPositionPercentOfTotal_019d8775-5d40-7fda-94c8-835ae8b881d9" xlink:href="unm-20260331.xsd#unm_FixedMaturitySecuritiesInUnrealizedLossPositionPercentOfTotal"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019d8775-5d40-78d6-8683-7581a8592b00" xlink:to="loc_unm_FixedMaturitySecuritiesInUnrealizedLossPositionPercentOfTotal_019d8775-5d40-7fda-94c8-835ae8b881d9" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.unum.com/role/DebtSecuritiesAvailableforsaleAllowanceforCreditLossesRollforwardDetails" xlink:type="simple" xlink:href="unm-20260331.xsd#DebtSecuritiesAvailableforsaleAllowanceforCreditLossesRollforwardDetails"/>
  <link:definitionLink xlink:role="http://www.unum.com/role/DebtSecuritiesAvailableforsaleAllowanceforCreditLossesRollforwardDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableforsaleAllowanceForCreditLossLineItems_019d8775-5d40-7ca4-b35b-16aa051481f6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableforsaleAllowanceForCreditLossLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLossTable_019d8775-5d40-75ef-9c01-313d800b8646" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLossTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtSecuritiesAvailableforsaleAllowanceForCreditLossLineItems_019d8775-5d40-7ca4-b35b-16aa051481f6" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLossTable_019d8775-5d40-75ef-9c01-313d800b8646" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_019d8775-5d40-7d62-83e0-d35236d20674" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLossTable_019d8775-5d40-75ef-9c01-313d800b8646" xlink:to="loc_us-gaap_FinancialInstrumentAxis_019d8775-5d40-7d62-83e0-d35236d20674" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5d40-7d62-83e0-d35236d20674_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019d8775-5d40-7d62-83e0-d35236d20674" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5d40-7d62-83e0-d35236d20674_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5d40-78b8-96f4-588327aacded" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019d8775-5d40-7d62-83e0-d35236d20674" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5d40-78b8-96f4-588327aacded" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllOtherCorporateBondsMember_019d8775-5d40-74e5-892e-a86484563eaf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllOtherCorporateBondsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5d40-78b8-96f4-588327aacded" xlink:to="loc_us-gaap_AllOtherCorporateBondsMember_019d8775-5d40-74e5-892e-a86484563eaf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLossRollForward_019d8775-5d40-735b-834a-051a13bff234" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLossRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtSecuritiesAvailableforsaleAllowanceForCreditLossLineItems_019d8775-5d40-7ca4-b35b-16aa051481f6" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLossRollForward_019d8775-5d40-735b-834a-051a13bff234" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLoss_019d8775-5d40-73ee-b904-2661d528736b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLossRollForward_019d8775-5d40-735b-834a-051a13bff234" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLoss_019d8775-5d40-73ee-b904-2661d528736b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLossNotPreviouslyRecorded_019d8775-5d40-7bd6-b129-e0a21005fc9a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLossNotPreviouslyRecorded"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLossRollForward_019d8775-5d40-735b-834a-051a13bff234" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLossNotPreviouslyRecorded_019d8775-5d40-7bd6-b129-e0a21005fc9a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLossSellBeforeRecovery_019dcad4-b598-7cc6-a0cc-f6290bbe5047" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLossSellBeforeRecovery"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLossRollForward_019d8775-5d40-735b-834a-051a13bff234" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLossSellBeforeRecovery_019dcad4-b598-7cc6-a0cc-f6290bbe5047" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLossNotToSellBeforeRecoveryCreditLossPreviouslyRecordedExpenseReversal_019d8775-5d40-7aa7-88e0-644e1dc0cc6b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLossNotToSellBeforeRecoveryCreditLossPreviouslyRecordedExpenseReversal"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLossRollForward_019d8775-5d40-735b-834a-051a13bff234" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLossNotToSellBeforeRecoveryCreditLossPreviouslyRecordedExpenseReversal_019d8775-5d40-7aa7-88e0-644e1dc0cc6b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLoss_019d8775-5d40-75e7-9412-62149f9406e1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLoss"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.unum.com/role/MortgageLoansbyPropertyTypeandGeographicRegionDetail" xlink:type="simple" xlink:href="unm-20260331.xsd#MortgageLoansbyPropertyTypeandGeographicRegionDetail"/>
  <link:definitionLink xlink:role="http://www.unum.com/role/MortgageLoansbyPropertyTypeandGeographicRegionDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_srt_MortgageLoansOnRealEstateLineItems_019d8775-5d40-71d3-a33f-7e8733aec46e" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MortgageLoansOnRealEstateLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MortgageLoansOnRealEstateScheduleTable_019d8775-5d40-7318-8bc2-5b3026662da9" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MortgageLoansOnRealEstateScheduleTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_srt_MortgageLoansOnRealEstateLineItems_019d8775-5d40-71d3-a33f-7e8733aec46e" xlink:to="loc_srt_MortgageLoansOnRealEstateScheduleTable_019d8775-5d40-7318-8bc2-5b3026662da9" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis_019d8775-5d40-7b57-89dc-2ad02caa5649" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_srt_MortgageLoansOnRealEstateScheduleTable_019d8775-5d40-7318-8bc2-5b3026662da9" xlink:to="loc_srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis_019d8775-5d40-7b57-89dc-2ad02caa5649" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_019d8775-5d40-7b57-89dc-2ad02caa5649_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MortgageLoansOnRealEstateNamePropertyTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis_019d8775-5d40-7b57-89dc-2ad02caa5649" xlink:to="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_019d8775-5d40-7b57-89dc-2ad02caa5649_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_019d8775-5d40-70ae-b37e-53b6baaf627a" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MortgageLoansOnRealEstateNamePropertyTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis_019d8775-5d40-7b57-89dc-2ad02caa5649" xlink:to="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_019d8775-5d40-70ae-b37e-53b6baaf627a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ApartmentBuildingMember_019d8775-5d40-729b-9cf3-7eb22e153e67" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ApartmentBuildingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_019d8775-5d40-70ae-b37e-53b6baaf627a" xlink:to="loc_srt_ApartmentBuildingMember_019d8775-5d40-729b-9cf3-7eb22e153e67" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_IndustrialPropertyMember_019d8775-5d40-753b-acd9-3676706647b4" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_IndustrialPropertyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_019d8775-5d40-70ae-b37e-53b6baaf627a" xlink:to="loc_srt_IndustrialPropertyMember_019d8775-5d40-753b-acd9-3676706647b4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OfficeBuildingMember_019d8775-5d40-7bd3-aac8-80fb5c077ba4" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_OfficeBuildingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_019d8775-5d40-70ae-b37e-53b6baaf627a" xlink:to="loc_srt_OfficeBuildingMember_019d8775-5d40-7bd3-aac8-80fb5c077ba4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RetailSiteMember_019d8775-5d40-7215-b9c6-b179e3a1f7da" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RetailSiteMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_019d8775-5d40-70ae-b37e-53b6baaf627a" xlink:to="loc_srt_RetailSiteMember_019d8775-5d40-7215-b9c6-b179e3a1f7da" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OtherPropertyMember_019d8775-5d40-7c88-b9b9-4d1949ac573e" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_OtherPropertyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_019d8775-5d40-70ae-b37e-53b6baaf627a" xlink:to="loc_srt_OtherPropertyMember_019d8775-5d40-7c88-b9b9-4d1949ac573e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_019d8775-5d40-736d-b677-c7ea24539fc9" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_srt_MortgageLoansOnRealEstateScheduleTable_019d8775-5d40-7318-8bc2-5b3026662da9" xlink:to="loc_srt_StatementGeographicalAxis_019d8775-5d40-736d-b677-c7ea24539fc9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_019d8775-5d40-736d-b677-c7ea24539fc9_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_019d8775-5d40-736d-b677-c7ea24539fc9" xlink:to="loc_srt_SegmentGeographicalDomain_019d8775-5d40-736d-b677-c7ea24539fc9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_019d8775-5d40-7938-9929-495c74bbed0d" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_019d8775-5d40-736d-b677-c7ea24539fc9" xlink:to="loc_srt_SegmentGeographicalDomain_019d8775-5d40-7938-9929-495c74bbed0d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_NewEnglandMember_019d8775-5d40-74c9-92d6-0c4f28a14a5a" xlink:href="unm-20260331.xsd#unm_NewEnglandMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019d8775-5d40-7938-9929-495c74bbed0d" xlink:to="loc_unm_NewEnglandMember_019d8775-5d40-74c9-92d6-0c4f28a14a5a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_MiddleAtlanticMember_019d8775-5d40-7222-8a9e-b4ab1b2ec64f" xlink:href="unm-20260331.xsd#unm_MiddleAtlanticMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019d8775-5d40-7938-9929-495c74bbed0d" xlink:to="loc_unm_MiddleAtlanticMember_019d8775-5d40-7222-8a9e-b4ab1b2ec64f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_EastNorthCentralMember_019d8775-5d40-7511-996f-6bca2e424561" xlink:href="unm-20260331.xsd#unm_EastNorthCentralMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019d8775-5d40-7938-9929-495c74bbed0d" xlink:to="loc_unm_EastNorthCentralMember_019d8775-5d40-7511-996f-6bca2e424561" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_WestNorthCentralMember_019d8775-5d40-7033-9dd8-52823634aa85" xlink:href="unm-20260331.xsd#unm_WestNorthCentralMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019d8775-5d40-7938-9929-495c74bbed0d" xlink:to="loc_unm_WestNorthCentralMember_019d8775-5d40-7033-9dd8-52823634aa85" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_SouthAtlanticMember_019d8775-5d40-7834-bbe0-bc7382a71845" xlink:href="unm-20260331.xsd#unm_SouthAtlanticMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019d8775-5d40-7938-9929-495c74bbed0d" xlink:to="loc_unm_SouthAtlanticMember_019d8775-5d40-7834-bbe0-bc7382a71845" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_EastSouthCentralMember_019d8775-5d40-7ff2-bcb1-926179692e76" xlink:href="unm-20260331.xsd#unm_EastSouthCentralMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019d8775-5d40-7938-9929-495c74bbed0d" xlink:to="loc_unm_EastSouthCentralMember_019d8775-5d40-7ff2-bcb1-926179692e76" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_WestSouthCentralMember_019d8775-5d40-7ba8-bc4e-14d2df04fd70" xlink:href="unm-20260331.xsd#unm_WestSouthCentralMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019d8775-5d40-7938-9929-495c74bbed0d" xlink:to="loc_unm_WestSouthCentralMember_019d8775-5d40-7ba8-bc4e-14d2df04fd70" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_MountainMember_019d8775-5d40-7557-9f96-7d24f0b68275" xlink:href="unm-20260331.xsd#unm_MountainMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019d8775-5d40-7938-9929-495c74bbed0d" xlink:to="loc_unm_MountainMember_019d8775-5d40-7557-9f96-7d24f0b68275" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_PacificMember_019d8775-5d40-752b-8d58-3627ebe95bdf" xlink:href="unm-20260331.xsd#unm_PacificMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019d8775-5d40-7938-9929-495c74bbed0d" xlink:to="loc_unm_PacificMember_019d8775-5d40-752b-8d58-3627ebe95bdf" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MortgageLoansOnRealEstateCommercialAndConsumerNet_019d8775-5d40-7600-8bfc-1beba1a4256f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MortgageLoansOnRealEstateCommercialAndConsumerNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateLineItems_019d8775-5d40-71d3-a33f-7e8733aec46e" xlink:to="loc_us-gaap_MortgageLoansOnRealEstateCommercialAndConsumerNet_019d8775-5d40-7600-8bfc-1beba1a4256f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_PercentageOfLoanPortfolio_019d8775-5d40-7b1c-ad1c-5aa2ea8106ef" xlink:href="unm-20260331.xsd#unm_PercentageOfLoanPortfolio"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateLineItems_019d8775-5d40-71d3-a33f-7e8733aec46e" xlink:to="loc_unm_PercentageOfLoanPortfolio_019d8775-5d40-7b1c-ad1c-5aa2ea8106ef" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.unum.com/role/ScheduleofParticipatingMortgageLoansbyInternalCreditRatingandLoantoValueDetails" xlink:type="simple" xlink:href="unm-20260331.xsd#ScheduleofParticipatingMortgageLoansbyInternalCreditRatingandLoantoValueDetails"/>
  <link:definitionLink xlink:role="http://www.unum.com/role/ScheduleofParticipatingMortgageLoansbyInternalCreditRatingandLoantoValueDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_srt_MortgageLoansOnRealEstateLineItems_019d8775-5d40-703a-a55c-8414465059aa" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MortgageLoansOnRealEstateLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MortgageLoansOnRealEstateScheduleTable_019d8775-5d40-7a18-ab79-3ab966431144" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MortgageLoansOnRealEstateScheduleTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_srt_MortgageLoansOnRealEstateLineItems_019d8775-5d40-703a-a55c-8414465059aa" xlink:to="loc_srt_MortgageLoansOnRealEstateScheduleTable_019d8775-5d40-7a18-ab79-3ab966431144" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InternalCreditAssessmentAxis_019d8775-5d40-75ac-9058-90e18d50b52f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InternalCreditAssessmentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_srt_MortgageLoansOnRealEstateScheduleTable_019d8775-5d40-7a18-ab79-3ab966431144" xlink:to="loc_us-gaap_InternalCreditAssessmentAxis_019d8775-5d40-75ac-9058-90e18d50b52f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InternalCreditAssessmentDomain_019d8775-5d40-75ac-9058-90e18d50b52f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InternalCreditAssessmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_InternalCreditAssessmentAxis_019d8775-5d40-75ac-9058-90e18d50b52f" xlink:to="loc_us-gaap_InternalCreditAssessmentDomain_019d8775-5d40-75ac-9058-90e18d50b52f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InternalCreditAssessmentDomain_019d8775-5d40-74b0-9426-448ee20efe33" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InternalCreditAssessmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_InternalCreditAssessmentAxis_019d8775-5d40-75ac-9058-90e18d50b52f" xlink:to="loc_us-gaap_InternalCreditAssessmentDomain_019d8775-5d40-74b0-9426-448ee20efe33" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_AACreditRatingMember_019d8775-5d40-7a2f-aded-e05dbfd2121b" xlink:href="unm-20260331.xsd#unm_AACreditRatingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InternalCreditAssessmentDomain_019d8775-5d40-74b0-9426-448ee20efe33" xlink:to="loc_unm_AACreditRatingMember_019d8775-5d40-7a2f-aded-e05dbfd2121b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_CreditRatingMember_019d8775-5d40-702a-86cb-352b41127ff0" xlink:href="unm-20260331.xsd#unm_CreditRatingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InternalCreditAssessmentDomain_019d8775-5d40-74b0-9426-448ee20efe33" xlink:to="loc_unm_CreditRatingMember_019d8775-5d40-702a-86cb-352b41127ff0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_BBBCreditRatingMember_019d8775-5d40-7292-8b8b-8646b1d2ac13" xlink:href="unm-20260331.xsd#unm_BBBCreditRatingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InternalCreditAssessmentDomain_019d8775-5d40-74b0-9426-448ee20efe33" xlink:to="loc_unm_BBBCreditRatingMember_019d8775-5d40-7292-8b8b-8646b1d2ac13" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_BBCreditRatingMember_019d8775-5d40-77b0-a3a3-626af978a7e1" xlink:href="unm-20260331.xsd#unm_BBCreditRatingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InternalCreditAssessmentDomain_019d8775-5d40-74b0-9426-448ee20efe33" xlink:to="loc_unm_BBCreditRatingMember_019d8775-5d40-77b0-a3a3-626af978a7e1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_BCreditRatingMember_019d8775-5d40-7cb2-9829-db50a1b7d1e6" xlink:href="unm-20260331.xsd#unm_BCreditRatingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InternalCreditAssessmentDomain_019d8775-5d40-74b0-9426-448ee20efe33" xlink:to="loc_unm_BCreditRatingMember_019d8775-5d40-7cb2-9829-db50a1b7d1e6" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoanToValueAxis_019d8775-5d40-79af-a975-fd424cd89d5d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LoanToValueAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_srt_MortgageLoansOnRealEstateScheduleTable_019d8775-5d40-7a18-ab79-3ab966431144" xlink:to="loc_us-gaap_LoanToValueAxis_019d8775-5d40-79af-a975-fd424cd89d5d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoanToValueDomain_019d8775-5d40-79af-a975-fd424cd89d5d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LoanToValueDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LoanToValueAxis_019d8775-5d40-79af-a975-fd424cd89d5d" xlink:to="loc_us-gaap_LoanToValueDomain_019d8775-5d40-79af-a975-fd424cd89d5d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoanToValueDomain_019d8775-5d40-77d7-8889-8713a44feedb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LoanToValueDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LoanToValueAxis_019d8775-5d40-79af-a975-fd424cd89d5d" xlink:to="loc_us-gaap_LoanToValueDomain_019d8775-5d40-77d7-8889-8713a44feedb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_LoanToValueRatioBelowOrEqualTo65PercentMember_019d8775-5d40-72d4-bc15-f7098b8a505d" xlink:href="unm-20260331.xsd#unm_LoanToValueRatioBelowOrEqualTo65PercentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LoanToValueDomain_019d8775-5d40-77d7-8889-8713a44feedb" xlink:to="loc_unm_LoanToValueRatioBelowOrEqualTo65PercentMember_019d8775-5d40-72d4-bc15-f7098b8a505d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_LoanToValueRatioAbove65To75PercentMember_019d8775-5d40-7522-be27-d2ed43ba2160" xlink:href="unm-20260331.xsd#unm_LoanToValueRatioAbove65To75PercentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LoanToValueDomain_019d8775-5d40-77d7-8889-8713a44feedb" xlink:to="loc_unm_LoanToValueRatioAbove65To75PercentMember_019d8775-5d40-7522-be27-d2ed43ba2160" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_LoanToValueRatioAbove75To85PercentMember_019d8775-5d40-753f-abdb-257a276cccf9" xlink:href="unm-20260331.xsd#unm_LoanToValueRatioAbove75To85PercentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LoanToValueDomain_019d8775-5d40-77d7-8889-8713a44feedb" xlink:to="loc_unm_LoanToValueRatioAbove75To85PercentMember_019d8775-5d40-753f-abdb-257a276cccf9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_LoanToValueRatioAbove85PercentMember_019d8775-5d40-7782-8b03-c1756156d7d8" xlink:href="unm-20260331.xsd#unm_LoanToValueRatioAbove85PercentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LoanToValueDomain_019d8775-5d40-77d7-8889-8713a44feedb" xlink:to="loc_unm_LoanToValueRatioAbove85PercentMember_019d8775-5d40-7782-8b03-c1756156d7d8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MortgageLoansOnRealEstateCommercialAndConsumerNet_019d8775-5d40-7504-b69d-f9b43516b951" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MortgageLoansOnRealEstateCommercialAndConsumerNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateLineItems_019d8775-5d40-703a-a55c-8414465059aa" xlink:to="loc_us-gaap_MortgageLoansOnRealEstateCommercialAndConsumerNet_019d8775-5d40-7504-b69d-f9b43516b951" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_PercentageOfLoanPortfolio_019d8775-5d40-771b-8431-941ef2ae8120" xlink:href="unm-20260331.xsd#unm_PercentageOfLoanPortfolio"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateLineItems_019d8775-5d40-703a-a55c-8414465059aa" xlink:to="loc_unm_PercentageOfLoanPortfolio_019d8775-5d40-771b-8431-941ef2ae8120" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.unum.com/role/MortgageLoansSortedbyApplicableCreditQualityIndicatorsDetail" xlink:type="simple" xlink:href="unm-20260331.xsd#MortgageLoansSortedbyApplicableCreditQualityIndicatorsDetail"/>
  <link:definitionLink xlink:role="http://www.unum.com/role/MortgageLoansSortedbyApplicableCreditQualityIndicatorsDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_srt_MortgageLoansOnRealEstateLineItems_019d8775-5d40-7005-bc03-1b8fd2bdf199" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MortgageLoansOnRealEstateLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable_019d8775-5d40-796d-a221-4f24942e2d07" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_srt_MortgageLoansOnRealEstateLineItems_019d8775-5d40-7005-bc03-1b8fd2bdf199" xlink:to="loc_us-gaap_ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable_019d8775-5d40-796d-a221-4f24942e2d07" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_019d8775-5d40-7886-a5b7-abc031478ea5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable_019d8775-5d40-796d-a221-4f24942e2d07" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_019d8775-5d40-7886-a5b7-abc031478ea5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_019d8775-5d40-7886-a5b7-abc031478ea5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_019d8775-5d40-7886-a5b7-abc031478ea5" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_019d8775-5d40-7886-a5b7-abc031478ea5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_019d8775-5d40-7c57-b30b-eae8d578b167" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_019d8775-5d40-7886-a5b7-abc031478ea5" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_019d8775-5d40-7c57-b30b-eae8d578b167" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialRealEstateMember_019d8775-5d40-7198-bfb7-135ec183cf83" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommercialRealEstateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_019d8775-5d40-7c57-b30b-eae8d578b167" xlink:to="loc_us-gaap_CommercialRealEstateMember_019d8775-5d40-7198-bfb7-135ec183cf83" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InternalCreditAssessmentAxis_019d8775-5d40-70da-90d0-f9ce31f94ad7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InternalCreditAssessmentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable_019d8775-5d40-796d-a221-4f24942e2d07" xlink:to="loc_us-gaap_InternalCreditAssessmentAxis_019d8775-5d40-70da-90d0-f9ce31f94ad7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InternalCreditAssessmentDomain_019d8775-5d40-70da-90d0-f9ce31f94ad7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InternalCreditAssessmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_InternalCreditAssessmentAxis_019d8775-5d40-70da-90d0-f9ce31f94ad7" xlink:to="loc_us-gaap_InternalCreditAssessmentDomain_019d8775-5d40-70da-90d0-f9ce31f94ad7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InternalCreditAssessmentDomain_019d8775-5d40-7949-8415-fd666bd91608" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InternalCreditAssessmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_InternalCreditAssessmentAxis_019d8775-5d40-70da-90d0-f9ce31f94ad7" xlink:to="loc_us-gaap_InternalCreditAssessmentDomain_019d8775-5d40-7949-8415-fd666bd91608" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_AACreditRatingMember_019d8775-5d40-7063-8120-045a22c64fed" xlink:href="unm-20260331.xsd#unm_AACreditRatingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InternalCreditAssessmentDomain_019d8775-5d40-7949-8415-fd666bd91608" xlink:to="loc_unm_AACreditRatingMember_019d8775-5d40-7063-8120-045a22c64fed" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_CreditRatingMember_019d8775-5d40-7603-a701-e27775a48383" xlink:href="unm-20260331.xsd#unm_CreditRatingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InternalCreditAssessmentDomain_019d8775-5d40-7949-8415-fd666bd91608" xlink:to="loc_unm_CreditRatingMember_019d8775-5d40-7603-a701-e27775a48383" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_BBBCreditRatingMember_019d8775-5d40-7e60-9f9c-9b9f38ff6727" xlink:href="unm-20260331.xsd#unm_BBBCreditRatingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InternalCreditAssessmentDomain_019d8775-5d40-7949-8415-fd666bd91608" xlink:to="loc_unm_BBBCreditRatingMember_019d8775-5d40-7e60-9f9c-9b9f38ff6727" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_BBCreditRatingMember_019d8775-5d40-7df7-a6ee-bddceff9edb8" xlink:href="unm-20260331.xsd#unm_BBCreditRatingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InternalCreditAssessmentDomain_019d8775-5d40-7949-8415-fd666bd91608" xlink:to="loc_unm_BBCreditRatingMember_019d8775-5d40-7df7-a6ee-bddceff9edb8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_BCreditRatingMember_019d8775-5d40-7fbc-a843-5b4a4977e668" xlink:href="unm-20260331.xsd#unm_BCreditRatingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InternalCreditAssessmentDomain_019d8775-5d40-7949-8415-fd666bd91608" xlink:to="loc_unm_BCreditRatingMember_019d8775-5d40-7fbc-a843-5b4a4977e668" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_FinancingReceivableOriginationPeriodAxis_019d8775-5d40-72f8-9e7c-6f09f1265b62" xlink:href="unm-20260331.xsd#unm_FinancingReceivableOriginationPeriodAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable_019d8775-5d40-796d-a221-4f24942e2d07" xlink:to="loc_unm_FinancingReceivableOriginationPeriodAxis_019d8775-5d40-72f8-9e7c-6f09f1265b62" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_FinancingReceivableOriginationPeriodDomain_019d8775-5d40-72f8-9e7c-6f09f1265b62_default" xlink:href="unm-20260331.xsd#unm_FinancingReceivableOriginationPeriodDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_unm_FinancingReceivableOriginationPeriodAxis_019d8775-5d40-72f8-9e7c-6f09f1265b62" xlink:to="loc_unm_FinancingReceivableOriginationPeriodDomain_019d8775-5d40-72f8-9e7c-6f09f1265b62_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_FinancingReceivableOriginationPeriodDomain_019d8775-5d40-78f6-96f5-c677d61b638e" xlink:href="unm-20260331.xsd#unm_FinancingReceivableOriginationPeriodDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_unm_FinancingReceivableOriginationPeriodAxis_019d8775-5d40-72f8-9e7c-6f09f1265b62" xlink:to="loc_unm_FinancingReceivableOriginationPeriodDomain_019d8775-5d40-78f6-96f5-c677d61b638e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_OriginatedFiveOrMoreYearsBeforeLastFiscalYearMember_019d8775-5d40-73dc-bd54-3d24b7c6c43e" xlink:href="unm-20260331.xsd#unm_OriginatedFiveOrMoreYearsBeforeLastFiscalYearMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_unm_FinancingReceivableOriginationPeriodDomain_019d8775-5d40-78f6-96f5-c677d61b638e" xlink:to="loc_unm_OriginatedFiveOrMoreYearsBeforeLastFiscalYearMember_019d8775-5d40-73dc-bd54-3d24b7c6c43e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_OriginatedFourYearsBeforeLastFiscalYearMember_019d8775-5d40-7191-a6e0-cbc51448e97f" xlink:href="unm-20260331.xsd#unm_OriginatedFourYearsBeforeLastFiscalYearMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_unm_FinancingReceivableOriginationPeriodDomain_019d8775-5d40-78f6-96f5-c677d61b638e" xlink:to="loc_unm_OriginatedFourYearsBeforeLastFiscalYearMember_019d8775-5d40-7191-a6e0-cbc51448e97f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_OriginatedThreeYearsBeforeLastFiscalYearMember_019d8775-5d40-7912-8074-08d07eb7370b" xlink:href="unm-20260331.xsd#unm_OriginatedThreeYearsBeforeLastFiscalYearMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_unm_FinancingReceivableOriginationPeriodDomain_019d8775-5d40-78f6-96f5-c677d61b638e" xlink:to="loc_unm_OriginatedThreeYearsBeforeLastFiscalYearMember_019d8775-5d40-7912-8074-08d07eb7370b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_OriginatedTwoYearsBeforeLastFiscalYearMember_019d8775-5d40-7dc7-9af9-5fc3531d103d" xlink:href="unm-20260331.xsd#unm_OriginatedTwoYearsBeforeLastFiscalYearMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_unm_FinancingReceivableOriginationPeriodDomain_019d8775-5d40-78f6-96f5-c677d61b638e" xlink:to="loc_unm_OriginatedTwoYearsBeforeLastFiscalYearMember_019d8775-5d40-7dc7-9af9-5fc3531d103d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_OriginatedInFiscalYearBeforeLatestFiscalYearMember_019d8775-5d40-7bef-8d99-d088a81de065" xlink:href="unm-20260331.xsd#unm_OriginatedInFiscalYearBeforeLatestFiscalYearMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_unm_FinancingReceivableOriginationPeriodDomain_019d8775-5d40-78f6-96f5-c677d61b638e" xlink:to="loc_unm_OriginatedInFiscalYearBeforeLatestFiscalYearMember_019d8775-5d40-7bef-8d99-d088a81de065" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_OriginatedInCurrentFiscalYearMember_019d8775-5d40-7c9b-84b4-280d9e4e9bc6" xlink:href="unm-20260331.xsd#unm_OriginatedInCurrentFiscalYearMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_unm_FinancingReceivableOriginationPeriodDomain_019d8775-5d40-78f6-96f5-c677d61b638e" xlink:to="loc_unm_OriginatedInCurrentFiscalYearMember_019d8775-5d40-7c9b-84b4-280d9e4e9bc6" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoanToValueAxis_019d8775-5d40-7c22-b7b0-392f417c54d8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LoanToValueAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable_019d8775-5d40-796d-a221-4f24942e2d07" xlink:to="loc_us-gaap_LoanToValueAxis_019d8775-5d40-7c22-b7b0-392f417c54d8" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoanToValueDomain_019d8775-5d40-7c22-b7b0-392f417c54d8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LoanToValueDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LoanToValueAxis_019d8775-5d40-7c22-b7b0-392f417c54d8" xlink:to="loc_us-gaap_LoanToValueDomain_019d8775-5d40-7c22-b7b0-392f417c54d8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoanToValueDomain_019d8775-5d40-7d18-a061-ee4b07624cec" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LoanToValueDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LoanToValueAxis_019d8775-5d40-7c22-b7b0-392f417c54d8" xlink:to="loc_us-gaap_LoanToValueDomain_019d8775-5d40-7d18-a061-ee4b07624cec" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_LoanToValueRatioBelowOrEqualTo65PercentMember_019d8775-5d40-7d55-9723-344b31b776ce" xlink:href="unm-20260331.xsd#unm_LoanToValueRatioBelowOrEqualTo65PercentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LoanToValueDomain_019d8775-5d40-7d18-a061-ee4b07624cec" xlink:to="loc_unm_LoanToValueRatioBelowOrEqualTo65PercentMember_019d8775-5d40-7d55-9723-344b31b776ce" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_LoanToValueRatioAbove65To75PercentMember_019d8775-5d40-77ec-80ee-3a4dd3f8a43f" xlink:href="unm-20260331.xsd#unm_LoanToValueRatioAbove65To75PercentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LoanToValueDomain_019d8775-5d40-7d18-a061-ee4b07624cec" xlink:to="loc_unm_LoanToValueRatioAbove65To75PercentMember_019d8775-5d40-77ec-80ee-3a4dd3f8a43f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_LoanToValueRatioAbove75To85PercentMember_019d8775-5d40-7fae-9ae9-1ba288932433" xlink:href="unm-20260331.xsd#unm_LoanToValueRatioAbove75To85PercentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LoanToValueDomain_019d8775-5d40-7d18-a061-ee4b07624cec" xlink:to="loc_unm_LoanToValueRatioAbove75To85PercentMember_019d8775-5d40-7fae-9ae9-1ba288932433" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_LoanToValueRatioAbove85PercentMember_019d8775-5d40-7baa-8ed2-5717b9575574" xlink:href="unm-20260331.xsd#unm_LoanToValueRatioAbove85PercentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LoanToValueDomain_019d8775-5d40-7d18-a061-ee4b07624cec" xlink:to="loc_unm_LoanToValueRatioAbove85PercentMember_019d8775-5d40-7baa-8ed2-5717b9575574" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableOriginatedFiveOrMoreYearsBeforeLatestFiscalYear_019d8775-5d40-773e-aaa9-cb246655432a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableOriginatedFiveOrMoreYearsBeforeLatestFiscalYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateLineItems_019d8775-5d40-7005-bc03-1b8fd2bdf199" xlink:to="loc_us-gaap_FinancingReceivableOriginatedFiveOrMoreYearsBeforeLatestFiscalYear_019d8775-5d40-773e-aaa9-cb246655432a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableOriginatedFourYearsBeforeLatestFiscalYear_019d8775-5d40-72b6-931a-11b59382da12" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableOriginatedFourYearsBeforeLatestFiscalYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateLineItems_019d8775-5d40-7005-bc03-1b8fd2bdf199" xlink:to="loc_us-gaap_FinancingReceivableOriginatedFourYearsBeforeLatestFiscalYear_019d8775-5d40-72b6-931a-11b59382da12" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableOriginatedThreeYearsBeforeLatestFiscalYear_019d8775-5d40-7944-b64a-6cbe81cc5b87" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableOriginatedThreeYearsBeforeLatestFiscalYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateLineItems_019d8775-5d40-7005-bc03-1b8fd2bdf199" xlink:to="loc_us-gaap_FinancingReceivableOriginatedThreeYearsBeforeLatestFiscalYear_019d8775-5d40-7944-b64a-6cbe81cc5b87" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableOriginatedTwoYearsBeforeLatestFiscalYear_019d8775-5d40-7f7d-826f-3bb4dbb04f67" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableOriginatedTwoYearsBeforeLatestFiscalYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateLineItems_019d8775-5d40-7005-bc03-1b8fd2bdf199" xlink:to="loc_us-gaap_FinancingReceivableOriginatedTwoYearsBeforeLatestFiscalYear_019d8775-5d40-7f7d-826f-3bb4dbb04f67" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableOriginatedInFiscalYearBeforeLatestFiscalYear_019d8775-5d40-75d2-aad8-9d775b8c5929" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableOriginatedInFiscalYearBeforeLatestFiscalYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateLineItems_019d8775-5d40-7005-bc03-1b8fd2bdf199" xlink:to="loc_us-gaap_FinancingReceivableOriginatedInFiscalYearBeforeLatestFiscalYear_019d8775-5d40-75d2-aad8-9d775b8c5929" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableOriginatedInCurrentFiscalYear_019d8775-5d40-7bc9-a6f6-9b15b0e9fb1c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableOriginatedInCurrentFiscalYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateLineItems_019d8775-5d40-7005-bc03-1b8fd2bdf199" xlink:to="loc_us-gaap_FinancingReceivableOriginatedInCurrentFiscalYear_019d8775-5d40-7bc9-a6f6-9b15b0e9fb1c" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NotesReceivableGross_019d8775-5d40-7d64-a14a-a7b973c45c77" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NotesReceivableGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateLineItems_019d8775-5d40-7005-bc03-1b8fd2bdf199" xlink:to="loc_us-gaap_NotesReceivableGross_019d8775-5d40-7d64-a14a-a7b973c45c77" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableAllowanceForCreditLosses_019d8775-5d40-7599-9fcf-d15c08325845" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableAllowanceForCreditLosses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateLineItems_019d8775-5d40-7005-bc03-1b8fd2bdf199" xlink:to="loc_us-gaap_FinancingReceivableAllowanceForCreditLosses_019d8775-5d40-7599-9fcf-d15c08325845" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MortgageLoansOnRealEstateCommercialAndConsumerNet_019d8775-5d40-7be2-b38c-805da6e94d90" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MortgageLoansOnRealEstateCommercialAndConsumerNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateLineItems_019d8775-5d40-7005-bc03-1b8fd2bdf199" xlink:to="loc_us-gaap_MortgageLoansOnRealEstateCommercialAndConsumerNet_019d8775-5d40-7be2-b38c-805da6e94d90" xlink:type="arc" order="8"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.unum.com/role/MortgageLoansAllowanceforCreditLossesRollforwardDetails" xlink:type="simple" xlink:href="unm-20260331.xsd#MortgageLoansAllowanceforCreditLossesRollforwardDetails"/>
  <link:definitionLink xlink:role="http://www.unum.com/role/MortgageLoansAllowanceforCreditLossesRollforwardDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems_019d8775-5d40-7c32-b4e4-27519cb412af" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable_019d8775-5d40-76b5-8304-e067f3eb3290" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems_019d8775-5d40-7c32-b4e4-27519cb412af" xlink:to="loc_us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable_019d8775-5d40-76b5-8304-e067f3eb3290" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_019d8775-5d40-7697-abc9-f8b01aa7bcca" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable_019d8775-5d40-76b5-8304-e067f3eb3290" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_019d8775-5d40-7697-abc9-f8b01aa7bcca" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_019d8775-5d40-7697-abc9-f8b01aa7bcca_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_019d8775-5d40-7697-abc9-f8b01aa7bcca" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_019d8775-5d40-7697-abc9-f8b01aa7bcca_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_019d8775-5d40-7642-b964-9364ac2b9e5d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_019d8775-5d40-7697-abc9-f8b01aa7bcca" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_019d8775-5d40-7642-b964-9364ac2b9e5d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialRealEstateMember_019d8775-5d40-7817-8ae7-69dcb6c754e9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommercialRealEstateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_019d8775-5d40-7642-b964-9364ac2b9e5d" xlink:to="loc_us-gaap_CommercialRealEstateMember_019d8775-5d40-7817-8ae7-69dcb6c754e9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoanToValueAxis_019d8775-5d40-7117-948f-6f09bb9e19e0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LoanToValueAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable_019d8775-5d40-76b5-8304-e067f3eb3290" xlink:to="loc_us-gaap_LoanToValueAxis_019d8775-5d40-7117-948f-6f09bb9e19e0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoanToValueDomain_019d8775-5d40-7117-948f-6f09bb9e19e0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LoanToValueDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LoanToValueAxis_019d8775-5d40-7117-948f-6f09bb9e19e0" xlink:to="loc_us-gaap_LoanToValueDomain_019d8775-5d40-7117-948f-6f09bb9e19e0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoanToValueDomain_019d8775-5d40-7302-a6b8-7def55abb910" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LoanToValueDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LoanToValueAxis_019d8775-5d40-7117-948f-6f09bb9e19e0" xlink:to="loc_us-gaap_LoanToValueDomain_019d8775-5d40-7302-a6b8-7def55abb910" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_LoanToValueRatioBelowOrEqualTo65PercentMember_019d8775-5d40-7621-9181-e5ba7f2c1bba" xlink:href="unm-20260331.xsd#unm_LoanToValueRatioBelowOrEqualTo65PercentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LoanToValueDomain_019d8775-5d40-7302-a6b8-7def55abb910" xlink:to="loc_unm_LoanToValueRatioBelowOrEqualTo65PercentMember_019d8775-5d40-7621-9181-e5ba7f2c1bba" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_LoanToValueRatioAbove65To75PercentMember_019d8775-5d40-71f1-a1fc-165f94182d92" xlink:href="unm-20260331.xsd#unm_LoanToValueRatioAbove65To75PercentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LoanToValueDomain_019d8775-5d40-7302-a6b8-7def55abb910" xlink:to="loc_unm_LoanToValueRatioAbove65To75PercentMember_019d8775-5d40-71f1-a1fc-165f94182d92" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_LoanToValueRatioAbove75To85PercentMember_019d8775-5d40-715d-9d65-ad127d88397f" xlink:href="unm-20260331.xsd#unm_LoanToValueRatioAbove75To85PercentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LoanToValueDomain_019d8775-5d40-7302-a6b8-7def55abb910" xlink:to="loc_unm_LoanToValueRatioAbove75To85PercentMember_019d8775-5d40-715d-9d65-ad127d88397f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_LoanToValueRatioAbove85PercentMember_019d8775-5d40-70f8-936a-5fdb0437b063" xlink:href="unm-20260331.xsd#unm_LoanToValueRatioAbove85PercentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LoanToValueDomain_019d8775-5d40-7302-a6b8-7def55abb910" xlink:to="loc_unm_LoanToValueRatioAbove85PercentMember_019d8775-5d40-70f8-936a-5fdb0437b063" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesRollForward_019d8775-5d40-702a-8011-de6ff897563e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableAllowanceForCreditLossesRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems_019d8775-5d40-7c32-b4e4-27519cb412af" xlink:to="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesRollForward_019d8775-5d40-702a-8011-de6ff897563e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableAllowanceForCreditLosses_019d8775-5d40-7469-b3a7-e5bdff9e6b72" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableAllowanceForCreditLosses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesRollForward_019d8775-5d40-702a-8011-de6ff897563e" xlink:to="loc_us-gaap_FinancingReceivableAllowanceForCreditLosses_019d8775-5d40-7469-b3a7-e5bdff9e6b72" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProvisionForLoanLossesExpensed_019d8775-5d40-79a2-9a97-8f99251f4828" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProvisionForLoanLossesExpensed"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesRollForward_019d8775-5d40-702a-8011-de6ff897563e" xlink:to="loc_us-gaap_ProvisionForLoanLossesExpensed_019d8775-5d40-79a2-9a97-8f99251f4828" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs_019d8775-5d40-72db-97bd-b05d14668a23" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesRollForward_019d8775-5d40-702a-8011-de6ff897563e" xlink:to="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs_019d8775-5d40-72db-97bd-b05d14668a23" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery_019d8775-5d40-799e-b039-674cb14ecc1a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesRollForward_019d8775-5d40-702a-8011-de6ff897563e" xlink:to="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery_019d8775-5d40-799e-b039-674cb14ecc1a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableAllowanceForCreditLosses_019d8775-5d40-7655-84ca-270679ffce17" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableAllowanceForCreditLosses"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.unum.com/role/InvestmentsRemainingContractualMaturityofSecurityLendingAgreementsDetails" xlink:type="simple" xlink:href="unm-20260331.xsd#InvestmentsRemainingContractualMaturityofSecurityLendingAgreementsDetails"/>
  <link:definitionLink xlink:role="http://www.unum.com/role/InvestmentsRemainingContractualMaturityofSecurityLendingAgreementsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransferOfCertainFinancialAssetsAccountedForAsSecuredBorrowingsLineItems_019d8775-5d40-790a-b551-9471d8f7168c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransferOfCertainFinancialAssetsAccountedForAsSecuredBorrowingsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransferOfCertainFinancialAssetsAccountedForAsSecuredBorrowingsTable_019d8775-5d40-7ce1-9530-0de4cdea738d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransferOfCertainFinancialAssetsAccountedForAsSecuredBorrowingsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_TransferOfCertainFinancialAssetsAccountedForAsSecuredBorrowingsLineItems_019d8775-5d40-790a-b551-9471d8f7168c" xlink:to="loc_us-gaap_TransferOfCertainFinancialAssetsAccountedForAsSecuredBorrowingsTable_019d8775-5d40-7ce1-9530-0de4cdea738d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_019d8775-5d40-7e3a-a126-9a2d939b2467" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_TransferOfCertainFinancialAssetsAccountedForAsSecuredBorrowingsTable_019d8775-5d40-7ce1-9530-0de4cdea738d" xlink:to="loc_us-gaap_FinancialInstrumentAxis_019d8775-5d40-7e3a-a126-9a2d939b2467" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5d40-7e3a-a126-9a2d939b2467_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019d8775-5d40-7e3a-a126-9a2d939b2467" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5d40-7e3a-a126-9a2d939b2467_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5d40-7e3e-a2a3-5632a17535df" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019d8775-5d40-7e3a-a126-9a2d939b2467" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5d40-7e3e-a2a3-5632a17535df" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USTreasuryAndGovernmentMember_019dcb69-35f1-773d-a92e-b6bebef9903f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_USTreasuryAndGovernmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5d40-7e3e-a2a3-5632a17535df" xlink:to="loc_us-gaap_USTreasuryAndGovernmentMember_019dcb69-35f1-773d-a92e-b6bebef9903f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PublicUtilityBondsMember_019d8775-5d40-7030-8906-ea28effe486e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PublicUtilityBondsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5d40-7e3e-a2a3-5632a17535df" xlink:to="loc_us-gaap_PublicUtilityBondsMember_019d8775-5d40-7030-8906-ea28effe486e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermInvestmentsMember_019d8775-5d40-7fc8-993d-d2fe4e63bb81" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShortTermInvestmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5d40-7e3e-a2a3-5632a17535df" xlink:to="loc_us-gaap_ShortTermInvestmentsMember_019d8775-5d40-7fc8-993d-d2fe4e63bb81" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllOtherCorporateBondsMember_019d8775-5d40-7d0a-afad-ead839fdbd3c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllOtherCorporateBondsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5d40-7e3e-a2a3-5632a17535df" xlink:to="loc_us-gaap_AllOtherCorporateBondsMember_019d8775-5d40-7d0a-afad-ead839fdbd3c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsSoldUnderAgreementsToRepurchaseMaturityPeriodsAxis_019d8775-5d40-71dd-ae29-1ddd5378ed0a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsSoldUnderAgreementsToRepurchaseMaturityPeriodsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_TransferOfCertainFinancialAssetsAccountedForAsSecuredBorrowingsTable_019d8775-5d40-7ce1-9530-0de4cdea738d" xlink:to="loc_us-gaap_AssetsSoldUnderAgreementsToRepurchaseMaturityPeriodsAxis_019d8775-5d40-71dd-ae29-1ddd5378ed0a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsSoldUnderAgreementsToRepurchaseMaturityPeriodDomain_019d8775-5d40-71dd-ae29-1ddd5378ed0a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsSoldUnderAgreementsToRepurchaseMaturityPeriodDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AssetsSoldUnderAgreementsToRepurchaseMaturityPeriodsAxis_019d8775-5d40-71dd-ae29-1ddd5378ed0a" xlink:to="loc_us-gaap_AssetsSoldUnderAgreementsToRepurchaseMaturityPeriodDomain_019d8775-5d40-71dd-ae29-1ddd5378ed0a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsSoldUnderAgreementsToRepurchaseMaturityPeriodDomain_019d8775-5d40-732d-b520-8da21aee5df3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsSoldUnderAgreementsToRepurchaseMaturityPeriodDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AssetsSoldUnderAgreementsToRepurchaseMaturityPeriodsAxis_019d8775-5d40-71dd-ae29-1ddd5378ed0a" xlink:to="loc_us-gaap_AssetsSoldUnderAgreementsToRepurchaseMaturityPeriodDomain_019d8775-5d40-732d-b520-8da21aee5df3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MaturityOvernightMember_019d8775-5d40-7741-91a8-93a14a108c0c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MaturityOvernightMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsSoldUnderAgreementsToRepurchaseMaturityPeriodDomain_019d8775-5d40-732d-b520-8da21aee5df3" xlink:to="loc_us-gaap_MaturityOvernightMember_019d8775-5d40-7741-91a8-93a14a108c0c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuritiesLoanedIncludingNotSubjectToMasterNettingArrangementAndAssetsOtherThanSecuritiesTransferred_019d8775-5d40-72fd-80ce-96ed4893272a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SecuritiesLoanedIncludingNotSubjectToMasterNettingArrangementAndAssetsOtherThanSecuritiesTransferred"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransferOfCertainFinancialAssetsAccountedForAsSecuredBorrowingsLineItems_019d8775-5d40-790a-b551-9471d8f7168c" xlink:to="loc_us-gaap_SecuritiesLoanedIncludingNotSubjectToMasterNettingArrangementAndAssetsOtherThanSecuritiesTransferred_019d8775-5d40-72fd-80ce-96ed4893272a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuritiesLoanedAndSecuritiesSoldUnderAgreementToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement_019d8775-5d40-78af-9213-07962bc3cba3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SecuritiesLoanedAndSecuritiesSoldUnderAgreementToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransferOfCertainFinancialAssetsAccountedForAsSecuredBorrowingsLineItems_019d8775-5d40-790a-b551-9471d8f7168c" xlink:to="loc_us-gaap_SecuritiesLoanedAndSecuritiesSoldUnderAgreementToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement_019d8775-5d40-78af-9213-07962bc3cba3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredBorrowingsGrossDifferenceAmount_019d8775-5d40-75f0-a2c4-7b2e0bfcd4e1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SecuredBorrowingsGrossDifferenceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransferOfCertainFinancialAssetsAccountedForAsSecuredBorrowingsLineItems_019d8775-5d40-790a-b551-9471d8f7168c" xlink:to="loc_us-gaap_SecuredBorrowingsGrossDifferenceAmount_019d8775-5d40-75f0-a2c4-7b2e0bfcd4e1" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.unum.com/role/InvestmentsFederalHomeLoanBankCarryingAmountCollateralPostedandAdvancesReceivedDetails" xlink:type="simple" xlink:href="unm-20260331.xsd#InvestmentsFederalHomeLoanBankCarryingAmountCollateralPostedandAdvancesReceivedDetails"/>
  <link:definitionLink xlink:role="http://www.unum.com/role/InvestmentsFederalHomeLoanBankCarryingAmountCollateralPostedandAdvancesReceivedDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_unm_FederalHomeLoanBankCarryingValueofCommonStockCollateralPostedandAdvancesLineItems_019d8775-5d40-7eb9-858f-8c7fcaf42fa2" xlink:href="unm-20260331.xsd#unm_FederalHomeLoanBankCarryingValueofCommonStockCollateralPostedandAdvancesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_FederalHomeLoanBankCarryingValueofCommonStockCollateralPostedandAdvancesTable_019d8775-5d40-7193-88e7-888970a50b2a" xlink:href="unm-20260331.xsd#unm_FederalHomeLoanBankCarryingValueofCommonStockCollateralPostedandAdvancesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_unm_FederalHomeLoanBankCarryingValueofCommonStockCollateralPostedandAdvancesLineItems_019d8775-5d40-7eb9-858f-8c7fcaf42fa2" xlink:to="loc_unm_FederalHomeLoanBankCarryingValueofCommonStockCollateralPostedandAdvancesTable_019d8775-5d40-7193-88e7-888970a50b2a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_019d8775-5d40-719a-b687-8a8672577eeb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_unm_FederalHomeLoanBankCarryingValueofCommonStockCollateralPostedandAdvancesTable_019d8775-5d40-7193-88e7-888970a50b2a" xlink:to="loc_us-gaap_FinancialInstrumentAxis_019d8775-5d40-719a-b687-8a8672577eeb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5d40-719a-b687-8a8672577eeb_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019d8775-5d40-719a-b687-8a8672577eeb" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5d40-719a-b687-8a8672577eeb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5d40-7667-9d84-de793c0dd123" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019d8775-5d40-719a-b687-8a8672577eeb" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5d40-7667-9d84-de793c0dd123" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesMember_019d8775-5d40-778d-a456-3ac5d29d396e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5d40-7667-9d84-de793c0dd123" xlink:to="loc_us-gaap_DebtSecuritiesMember_019d8775-5d40-778d-a456-3ac5d29d396e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MortgageBackedSecuritiesMember_019d8775-5d40-7866-b139-73ba73d092cc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MortgageBackedSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5d40-7667-9d84-de793c0dd123" xlink:to="loc_us-gaap_MortgageBackedSecuritiesMember_019d8775-5d40-7866-b139-73ba73d092cc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FederalHomeLoanBankStock_019d8775-5d40-7f4d-8c2b-5e68030afc8f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FederalHomeLoanBankStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_unm_FederalHomeLoanBankCarryingValueofCommonStockCollateralPostedandAdvancesLineItems_019d8775-5d40-7eb9-858f-8c7fcaf42fa2" xlink:to="loc_us-gaap_FederalHomeLoanBankStock_019d8775-5d40-7f4d-8c2b-5e68030afc8f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FederalHomeLoanBankAdvancesBranchOfFHLBBankAmountOfAdvancesByBranch_019d8775-5d40-70d7-be59-97e43fafb8a2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FederalHomeLoanBankAdvancesBranchOfFHLBBankAmountOfAdvancesByBranch"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_unm_FederalHomeLoanBankCarryingValueofCommonStockCollateralPostedandAdvancesLineItems_019d8775-5d40-7eb9-858f-8c7fcaf42fa2" xlink:to="loc_us-gaap_FederalHomeLoanBankAdvancesBranchOfFHLBBankAmountOfAdvancesByBranch_019d8775-5d40-70d7-be59-97e43fafb8a2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresCollateralPledged1_019d8775-5d40-75db-b810-c63a72b1fa8c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresCollateralPledged1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_unm_FederalHomeLoanBankCarryingValueofCommonStockCollateralPostedandAdvancesLineItems_019d8775-5d40-7eb9-858f-8c7fcaf42fa2" xlink:to="loc_us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresCollateralPledged1_019d8775-5d40-75db-b810-c63a72b1fa8c" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.unum.com/role/InvestmentsScheduleofFinancialInstrumentandDerivativeOffsettingDetails" xlink:type="simple" xlink:href="unm-20260331.xsd#InvestmentsScheduleofFinancialInstrumentandDerivativeOffsettingDetails"/>
  <link:definitionLink xlink:role="http://www.unum.com/role/InvestmentsScheduleofFinancialInstrumentandDerivativeOffsettingDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OffsettingAssetsLineItems_019d8775-5d40-763f-a6c6-bbfa1f5c47e5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OffsettingAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OffsettingAssetsTable_019d8775-5d40-7a2c-86d8-7abcf76011d0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OffsettingAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_OffsettingAssetsLineItems_019d8775-5d40-763f-a6c6-bbfa1f5c47e5" xlink:to="loc_us-gaap_OffsettingAssetsTable_019d8775-5d40-7a2c-86d8-7abcf76011d0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransactionTypeAxis_019d8775-5d40-7227-a190-fdebe7a3871a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransactionTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_OffsettingAssetsTable_019d8775-5d40-7a2c-86d8-7abcf76011d0" xlink:to="loc_us-gaap_TransactionTypeAxis_019d8775-5d40-7227-a190-fdebe7a3871a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransactionDomain_019d8775-5d40-7227-a190-fdebe7a3871a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TransactionTypeAxis_019d8775-5d40-7227-a190-fdebe7a3871a" xlink:to="loc_us-gaap_TransactionDomain_019d8775-5d40-7227-a190-fdebe7a3871a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransactionDomain_019d8775-5d40-73f2-9fcc-a79f438d43a9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TransactionTypeAxis_019d8775-5d40-7227-a190-fdebe7a3871a" xlink:to="loc_us-gaap_TransactionDomain_019d8775-5d40-73f2-9fcc-a79f438d43a9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OverTheCounterMember_019d8775-5d40-7290-93d5-21beea1f0cfc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OverTheCounterMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransactionDomain_019d8775-5d40-73f2-9fcc-a79f438d43a9" xlink:to="loc_us-gaap_OverTheCounterMember_019d8775-5d40-7290-93d5-21beea1f0cfc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OffsettingDerivativeAssetsAbstract_019d8775-5d40-7b4b-9722-32ee355c141d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OffsettingDerivativeAssetsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OffsettingAssetsLineItems_019d8775-5d40-763f-a6c6-bbfa1f5c47e5" xlink:to="loc_us-gaap_OffsettingDerivativeAssetsAbstract_019d8775-5d40-7b4b-9722-32ee355c141d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeFairValueOfDerivativeAsset_019d8775-5d40-7b2d-9f1b-55f09fc770e6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeFairValueOfDerivativeAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OffsettingDerivativeAssetsAbstract_019d8775-5d40-7b4b-9722-32ee355c141d" xlink:to="loc_us-gaap_DerivativeFairValueOfDerivativeAsset_019d8775-5d40-7b2d-9f1b-55f09fc770e6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssetFairValueGrossLiability_019d8775-5d40-7010-a6ae-15ee78d1d8da" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeAssetFairValueGrossLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OffsettingDerivativeAssetsAbstract_019d8775-5d40-7b4b-9722-32ee355c141d" xlink:to="loc_us-gaap_DerivativeAssetFairValueGrossLiability_019d8775-5d40-7010-a6ae-15ee78d1d8da" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssets_019d8775-5d40-768f-b36d-17d49f84e030" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OffsettingDerivativeAssetsAbstract_019d8775-5d40-7b4b-9722-32ee355c141d" xlink:to="loc_us-gaap_DerivativeAssets_019d8775-5d40-768f-b36d-17d49f84e030" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeCollateralObligationToReturnSecurities_019d8775-5d40-7bec-a0d3-951f8c067533" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeCollateralObligationToReturnSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OffsettingDerivativeAssetsAbstract_019d8775-5d40-7b4b-9722-32ee355c141d" xlink:to="loc_us-gaap_DerivativeCollateralObligationToReturnSecurities_019d8775-5d40-7bec-a0d3-951f8c067533" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeCollateralObligationToReturnCash_019d8775-5d40-77a6-a5c2-42e7359f959b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeCollateralObligationToReturnCash"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OffsettingDerivativeAssetsAbstract_019d8775-5d40-7b4b-9722-32ee355c141d" xlink:to="loc_us-gaap_DerivativeCollateralObligationToReturnCash_019d8775-5d40-77a6-a5c2-42e7359f959b" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeFairValueOfDerivativeAssetAmountOffsetAgainstCollateral_019d8775-5d40-7596-8d9d-b63db0c08788" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeFairValueOfDerivativeAssetAmountOffsetAgainstCollateral"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OffsettingDerivativeAssetsAbstract_019d8775-5d40-7b4b-9722-32ee355c141d" xlink:to="loc_us-gaap_DerivativeFairValueOfDerivativeAssetAmountOffsetAgainstCollateral_019d8775-5d40-7596-8d9d-b63db0c08788" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OffsettingSecuritiesLoanedAbstract_019d8775-5d40-7c5a-9426-539da1877c32" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OffsettingSecuritiesLoanedAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OffsettingAssetsLineItems_019d8775-5d40-763f-a6c6-bbfa1f5c47e5" xlink:to="loc_us-gaap_OffsettingSecuritiesLoanedAbstract_019d8775-5d40-7c5a-9426-539da1877c32" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuritiesLoanedGross_019d8775-5d40-7691-89d2-45cc5a9ac18e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SecuritiesLoanedGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OffsettingSecuritiesLoanedAbstract_019d8775-5d40-7c5a-9426-539da1877c32" xlink:to="loc_us-gaap_SecuritiesLoanedGross_019d8775-5d40-7691-89d2-45cc5a9ac18e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuritiesLoanedAsset_019d8775-5d40-7060-8d09-0eb823414adc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SecuritiesLoanedAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OffsettingSecuritiesLoanedAbstract_019d8775-5d40-7c5a-9426-539da1877c32" xlink:to="loc_us-gaap_SecuritiesLoanedAsset_019d8775-5d40-7060-8d09-0eb823414adc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuritiesLoaned_019d8775-5d40-73a4-a482-dfea32570aa7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SecuritiesLoaned"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OffsettingSecuritiesLoanedAbstract_019d8775-5d40-7c5a-9426-539da1877c32" xlink:to="loc_us-gaap_SecuritiesLoaned_019d8775-5d40-73a4-a482-dfea32570aa7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuritiesLoanedCollateralRightToReclaimSecurities_019d8775-5d40-7ffc-b6cd-0390420a61fe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SecuritiesLoanedCollateralRightToReclaimSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OffsettingSecuritiesLoanedAbstract_019d8775-5d40-7c5a-9426-539da1877c32" xlink:to="loc_us-gaap_SecuritiesLoanedCollateralRightToReclaimSecurities_019d8775-5d40-7ffc-b6cd-0390420a61fe" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuritiesLoanedCollateralRightToReclaimCash_019d8775-5d40-709b-8e65-7243b1983fea" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SecuritiesLoanedCollateralRightToReclaimCash"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OffsettingSecuritiesLoanedAbstract_019d8775-5d40-7c5a-9426-539da1877c32" xlink:to="loc_us-gaap_SecuritiesLoanedCollateralRightToReclaimCash_019d8775-5d40-709b-8e65-7243b1983fea" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuritiesLoanedAmountOffsetAgainstCollateral_019d8775-5d40-7300-905b-790bf5816875" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SecuritiesLoanedAmountOffsetAgainstCollateral"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OffsettingSecuritiesLoanedAbstract_019d8775-5d40-7c5a-9426-539da1877c32" xlink:to="loc_us-gaap_SecuritiesLoanedAmountOffsetAgainstCollateral_019d8775-5d40-7300-905b-790bf5816875" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OffsettingDerivativeAssetSecuritiesPurchasedUnderAgreementsToResellSecuritiesBorrowedAbstract_019d8775-5d40-7f2f-ba63-0884bceacec4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OffsettingDerivativeAssetSecuritiesPurchasedUnderAgreementsToResellSecuritiesBorrowedAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OffsettingAssetsLineItems_019d8775-5d40-763f-a6c6-bbfa1f5c47e5" xlink:to="loc_us-gaap_OffsettingDerivativeAssetSecuritiesPurchasedUnderAgreementsToResellSecuritiesBorrowedAbstract_019d8775-5d40-7f2f-ba63-0884bceacec4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssetSecuritiesPurchasedUnderAgreementsToResellSecuritiesBorrowedGross_019d8775-5d40-7f0a-8f6b-4a73dc4e863b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeAssetSecuritiesPurchasedUnderAgreementsToResellSecuritiesBorrowedGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OffsettingDerivativeAssetSecuritiesPurchasedUnderAgreementsToResellSecuritiesBorrowedAbstract_019d8775-5d40-7f2f-ba63-0884bceacec4" xlink:to="loc_us-gaap_DerivativeAssetSecuritiesPurchasedUnderAgreementsToResellSecuritiesBorrowedGross_019d8775-5d40-7f0a-8f6b-4a73dc4e863b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssetSecuritiesPurchasedUnderAgreementsToResellSecuritiesBorrowedLiability_019d8775-5d40-765c-82a6-30ec9c9647aa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeAssetSecuritiesPurchasedUnderAgreementsToResellSecuritiesBorrowedLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OffsettingDerivativeAssetSecuritiesPurchasedUnderAgreementsToResellSecuritiesBorrowedAbstract_019d8775-5d40-7f2f-ba63-0884bceacec4" xlink:to="loc_us-gaap_DerivativeAssetSecuritiesPurchasedUnderAgreementsToResellSecuritiesBorrowedLiability_019d8775-5d40-765c-82a6-30ec9c9647aa" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssetSecuritiesPurchasedUnderAgreementsToResellSecuritiesBorrowed_019d8775-5d40-74f4-bb73-49eee95834f6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeAssetSecuritiesPurchasedUnderAgreementsToResellSecuritiesBorrowed"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OffsettingDerivativeAssetSecuritiesPurchasedUnderAgreementsToResellSecuritiesBorrowedAbstract_019d8775-5d40-7f2f-ba63-0884bceacec4" xlink:to="loc_us-gaap_DerivativeAssetSecuritiesPurchasedUnderAgreementsToResellSecuritiesBorrowed_019d8775-5d40-74f4-bb73-49eee95834f6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssetSecuritiesPurchasedUnderAgreementsToResellSecuritiesBorrowedCollateralObligationToReturnSecurities_019d8775-5d40-7f90-bc04-c1539c63c980" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeAssetSecuritiesPurchasedUnderAgreementsToResellSecuritiesBorrowedCollateralObligationToReturnSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OffsettingDerivativeAssetSecuritiesPurchasedUnderAgreementsToResellSecuritiesBorrowedAbstract_019d8775-5d40-7f2f-ba63-0884bceacec4" xlink:to="loc_us-gaap_DerivativeAssetSecuritiesPurchasedUnderAgreementsToResellSecuritiesBorrowedCollateralObligationToReturnSecurities_019d8775-5d40-7f90-bc04-c1539c63c980" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssetSecuritiesPurchasedUnderAgreementsToResellSecuritiesBorrowedCollateralObligationToReturnCash_019d8775-5d40-7839-9dd5-9d851a854ba3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeAssetSecuritiesPurchasedUnderAgreementsToResellSecuritiesBorrowedCollateralObligationToReturnCash"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OffsettingDerivativeAssetSecuritiesPurchasedUnderAgreementsToResellSecuritiesBorrowedAbstract_019d8775-5d40-7f2f-ba63-0884bceacec4" xlink:to="loc_us-gaap_DerivativeAssetSecuritiesPurchasedUnderAgreementsToResellSecuritiesBorrowedCollateralObligationToReturnCash_019d8775-5d40-7839-9dd5-9d851a854ba3" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssetSecuritiesPurchasedUnderAgreementsToResellSecuritiesBorrowedAmountOffsetAgainstCollateral_019d8775-5d40-7a7b-9476-d007b6a1afda" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeAssetSecuritiesPurchasedUnderAgreementsToResellSecuritiesBorrowedAmountOffsetAgainstCollateral"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OffsettingDerivativeAssetSecuritiesPurchasedUnderAgreementsToResellSecuritiesBorrowedAbstract_019d8775-5d40-7f2f-ba63-0884bceacec4" xlink:to="loc_us-gaap_DerivativeAssetSecuritiesPurchasedUnderAgreementsToResellSecuritiesBorrowedAmountOffsetAgainstCollateral_019d8775-5d40-7a7b-9476-d007b6a1afda" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OffsettingLiabilitiesLineItems_019d8775-5d40-789c-add3-c73f43b348c0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OffsettingLiabilitiesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OffsettingLiabilitiesTable_019d8775-5d40-7c60-9a3b-6e05a29ea3c3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OffsettingLiabilitiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_OffsettingLiabilitiesLineItems_019d8775-5d40-789c-add3-c73f43b348c0" xlink:to="loc_us-gaap_OffsettingLiabilitiesTable_019d8775-5d40-7c60-9a3b-6e05a29ea3c3" xlink:type="arc" order="2" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransactionTypeAxis_019d8775-5d40-7b79-96c4-ef04caa9ad44" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransactionTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_OffsettingLiabilitiesTable_019d8775-5d40-7c60-9a3b-6e05a29ea3c3" xlink:to="loc_us-gaap_TransactionTypeAxis_019d8775-5d40-7b79-96c4-ef04caa9ad44" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransactionDomain_019d8775-5d40-7b79-96c4-ef04caa9ad44_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransactionDomain"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransactionDomain_019d8775-5d40-7865-b01d-ea8bf9cf7cba" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransactionDomain"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OverTheCounterMember_019d8775-5d40-72a5-9432-d62949ea04e0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OverTheCounterMember"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OffsettingDerivativeLiabilitiesAbstract_019d8775-5d40-76f3-9916-27ab14c9c312" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OffsettingDerivativeLiabilitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OffsettingLiabilitiesLineItems_019d8775-5d40-789c-add3-c73f43b348c0" xlink:to="loc_us-gaap_OffsettingDerivativeLiabilitiesAbstract_019d8775-5d40-76f3-9916-27ab14c9c312" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeFairValueOfDerivativeLiability_019d8775-5d40-78a0-8947-a37b9a09e524" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeFairValueOfDerivativeLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OffsettingDerivativeLiabilitiesAbstract_019d8775-5d40-76f3-9916-27ab14c9c312" xlink:to="loc_us-gaap_DerivativeFairValueOfDerivativeLiability_019d8775-5d40-78a0-8947-a37b9a09e524" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLiabilityFairValueGrossAsset_019d8775-5d40-7501-9d6c-ca1453d2c145" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeLiabilityFairValueGrossAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OffsettingDerivativeLiabilitiesAbstract_019d8775-5d40-76f3-9916-27ab14c9c312" xlink:to="loc_us-gaap_DerivativeLiabilityFairValueGrossAsset_019d8775-5d40-7501-9d6c-ca1453d2c145" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLiabilities_019d8775-5d40-7a0b-929d-2505392e496b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OffsettingDerivativeLiabilitiesAbstract_019d8775-5d40-76f3-9916-27ab14c9c312" xlink:to="loc_us-gaap_DerivativeLiabilities_019d8775-5d40-7a0b-929d-2505392e496b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeCollateralRightToReclaimSecurities_019d8775-5d40-7f17-895a-e7e7fd6f7426" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeCollateralRightToReclaimSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OffsettingDerivativeLiabilitiesAbstract_019d8775-5d40-76f3-9916-27ab14c9c312" xlink:to="loc_us-gaap_DerivativeCollateralRightToReclaimSecurities_019d8775-5d40-7f17-895a-e7e7fd6f7426" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeCollateralRightToReclaimCash_019d8775-5d40-71aa-bf0a-f8bd5eb86b14" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeCollateralRightToReclaimCash"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OffsettingDerivativeLiabilitiesAbstract_019d8775-5d40-76f3-9916-27ab14c9c312" xlink:to="loc_us-gaap_DerivativeCollateralRightToReclaimCash_019d8775-5d40-71aa-bf0a-f8bd5eb86b14" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeFairValueOfDerivativeLiabilityAmountOffsetAgainstCollateral_019d8775-5d40-78fd-aef7-98203d671b14" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeFairValueOfDerivativeLiabilityAmountOffsetAgainstCollateral"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OffsettingDerivativeLiabilitiesAbstract_019d8775-5d40-76f3-9916-27ab14c9c312" xlink:to="loc_us-gaap_DerivativeFairValueOfDerivativeLiabilityAmountOffsetAgainstCollateral_019d8775-5d40-78fd-aef7-98203d671b14" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OffsettingSecuritiesBorrowedAbstract_019d8775-5d40-797a-9344-740a13a0ccc6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OffsettingSecuritiesBorrowedAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OffsettingLiabilitiesLineItems_019d8775-5d40-789c-add3-c73f43b348c0" xlink:to="loc_us-gaap_OffsettingSecuritiesBorrowedAbstract_019d8775-5d40-797a-9344-740a13a0ccc6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuritiesBorrowedGross_019d8775-5d40-7f98-b00b-5e8f7b8a597e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SecuritiesBorrowedGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OffsettingSecuritiesBorrowedAbstract_019d8775-5d40-797a-9344-740a13a0ccc6" xlink:to="loc_us-gaap_SecuritiesBorrowedGross_019d8775-5d40-7f98-b00b-5e8f7b8a597e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuritiesBorrowedLiability_019d8775-5d40-74fd-b068-56ecbe448909" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SecuritiesBorrowedLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OffsettingSecuritiesBorrowedAbstract_019d8775-5d40-797a-9344-740a13a0ccc6" xlink:to="loc_us-gaap_SecuritiesBorrowedLiability_019d8775-5d40-74fd-b068-56ecbe448909" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuritiesBorrowed_019d8775-5d40-71ca-bfc1-2717b0e552e8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SecuritiesBorrowed"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OffsettingSecuritiesBorrowedAbstract_019d8775-5d40-797a-9344-740a13a0ccc6" xlink:to="loc_us-gaap_SecuritiesBorrowed_019d8775-5d40-71ca-bfc1-2717b0e552e8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuritiesBorrowedCollateralObligationToReturnSecurities_019d8775-5d40-7f41-a58e-4f62554fded2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SecuritiesBorrowedCollateralObligationToReturnSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OffsettingSecuritiesBorrowedAbstract_019d8775-5d40-797a-9344-740a13a0ccc6" xlink:to="loc_us-gaap_SecuritiesBorrowedCollateralObligationToReturnSecurities_019d8775-5d40-7f41-a58e-4f62554fded2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuritiesBorrowedCollateralObligationToReturnCash_019d8775-5d40-79fb-8615-a14be979cb60" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SecuritiesBorrowedCollateralObligationToReturnCash"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OffsettingSecuritiesBorrowedAbstract_019d8775-5d40-797a-9344-740a13a0ccc6" xlink:to="loc_us-gaap_SecuritiesBorrowedCollateralObligationToReturnCash_019d8775-5d40-79fb-8615-a14be979cb60" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuritiesBorrowedAmountOffsetAgainstCollateral_019d8775-5d40-7290-b37c-4c590b5d5af1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SecuritiesBorrowedAmountOffsetAgainstCollateral"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OffsettingSecuritiesBorrowedAbstract_019d8775-5d40-797a-9344-740a13a0ccc6" xlink:to="loc_us-gaap_SecuritiesBorrowedAmountOffsetAgainstCollateral_019d8775-5d40-7290-b37c-4c590b5d5af1" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OffsettingDerivativeLiabilitySecuritiesSoldUnderAgreementsToResellSecuritiesLoanedAbstract_019d8775-5d40-7577-b230-05ee9220ccbf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OffsettingDerivativeLiabilitySecuritiesSoldUnderAgreementsToResellSecuritiesLoanedAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OffsettingLiabilitiesLineItems_019d8775-5d40-789c-add3-c73f43b348c0" xlink:to="loc_us-gaap_OffsettingDerivativeLiabilitySecuritiesSoldUnderAgreementsToResellSecuritiesLoanedAbstract_019d8775-5d40-7577-b230-05ee9220ccbf" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLiabilitySecuritiesSoldUnderAgreementsToResellSecuritiesLoanedGross_019d8775-5d40-7255-925b-1421934295da" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeLiabilitySecuritiesSoldUnderAgreementsToResellSecuritiesLoanedGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OffsettingDerivativeLiabilitySecuritiesSoldUnderAgreementsToResellSecuritiesLoanedAbstract_019d8775-5d40-7577-b230-05ee9220ccbf" xlink:to="loc_us-gaap_DerivativeLiabilitySecuritiesSoldUnderAgreementsToResellSecuritiesLoanedGross_019d8775-5d40-7255-925b-1421934295da" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLiabilitySecuritiesSoldUnderAgreementsToResellSecuritiesLoanedAsset_019d8775-5d40-76b8-a055-daf7f729bce7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeLiabilitySecuritiesSoldUnderAgreementsToResellSecuritiesLoanedAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OffsettingDerivativeLiabilitySecuritiesSoldUnderAgreementsToResellSecuritiesLoanedAbstract_019d8775-5d40-7577-b230-05ee9220ccbf" xlink:to="loc_us-gaap_DerivativeLiabilitySecuritiesSoldUnderAgreementsToResellSecuritiesLoanedAsset_019d8775-5d40-76b8-a055-daf7f729bce7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLiabilitySecuritiesSoldUnderAgreementsToResellSecuritiesLoaned_019d8775-5d40-7300-9636-d31f75be78ad" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeLiabilitySecuritiesSoldUnderAgreementsToResellSecuritiesLoaned"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OffsettingDerivativeLiabilitySecuritiesSoldUnderAgreementsToResellSecuritiesLoanedAbstract_019d8775-5d40-7577-b230-05ee9220ccbf" xlink:to="loc_us-gaap_DerivativeLiabilitySecuritiesSoldUnderAgreementsToResellSecuritiesLoaned_019d8775-5d40-7300-9636-d31f75be78ad" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLiabilitySecuritiesSoldUnderAgreementsToResellSecuritiesLoanedCollateralRightToReclaimSecurities_019d8775-5d40-7514-be9b-fe50d8eef8f4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeLiabilitySecuritiesSoldUnderAgreementsToResellSecuritiesLoanedCollateralRightToReclaimSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OffsettingDerivativeLiabilitySecuritiesSoldUnderAgreementsToResellSecuritiesLoanedAbstract_019d8775-5d40-7577-b230-05ee9220ccbf" xlink:to="loc_us-gaap_DerivativeLiabilitySecuritiesSoldUnderAgreementsToResellSecuritiesLoanedCollateralRightToReclaimSecurities_019d8775-5d40-7514-be9b-fe50d8eef8f4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLiabilitySecuritiesSoldUnderAgreementsToResellSecuritiesLoanedCollateralRightToReclaimCash_019d8775-5d40-7524-b531-e359a4fb0d91" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeLiabilitySecuritiesSoldUnderAgreementsToResellSecuritiesLoanedCollateralRightToReclaimCash"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OffsettingDerivativeLiabilitySecuritiesSoldUnderAgreementsToResellSecuritiesLoanedAbstract_019d8775-5d40-7577-b230-05ee9220ccbf" xlink:to="loc_us-gaap_DerivativeLiabilitySecuritiesSoldUnderAgreementsToResellSecuritiesLoanedCollateralRightToReclaimCash_019d8775-5d40-7524-b531-e359a4fb0d91" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLiabilitySecuritiesSoldUnderAgreementsToResellSecuritiesLoanedAmountOffsetAgainstCollateral_019d8775-5d40-72a4-abba-78f264d807c8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeLiabilitySecuritiesSoldUnderAgreementsToResellSecuritiesLoanedAmountOffsetAgainstCollateral"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OffsettingDerivativeLiabilitySecuritiesSoldUnderAgreementsToResellSecuritiesLoanedAbstract_019d8775-5d40-7577-b230-05ee9220ccbf" xlink:to="loc_us-gaap_DerivativeLiabilitySecuritiesSoldUnderAgreementsToResellSecuritiesLoanedAmountOffsetAgainstCollateral_019d8775-5d40-72a4-abba-78f264d807c8" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.unum.com/role/InvestmentsInvestmentIncomeDetail" xlink:type="simple" xlink:href="unm-20260331.xsd#InvestmentsInvestmentIncomeDetail"/>
  <link:definitionLink xlink:role="http://www.unum.com/role/InvestmentsInvestmentIncomeDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_019d8775-5d40-7e27-9720-431ad962ac4c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryTable_019d8775-5d40-746e-a504-0d44037bcccd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_019d8775-5d40-7e27-9720-431ad962ac4c" xlink:to="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryTable_019d8775-5d40-746e-a504-0d44037bcccd" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeAxis_019d8775-5d40-7556-8ca7-ce5cae7f9f84" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryTable_019d8775-5d40-746e-a504-0d44037bcccd" xlink:to="loc_us-gaap_InvestmentTypeAxis_019d8775-5d40-7556-8ca7-ce5cae7f9f84" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeCategorizationMember_019d8775-5d40-7556-8ca7-ce5cae7f9f84_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentTypeCategorizationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_InvestmentTypeAxis_019d8775-5d40-7556-8ca7-ce5cae7f9f84" xlink:to="loc_us-gaap_InvestmentTypeCategorizationMember_019d8775-5d40-7556-8ca7-ce5cae7f9f84_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeCategorizationMember_019d8775-5d40-70a7-9655-f17d563b6aaf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentTypeCategorizationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_InvestmentTypeAxis_019d8775-5d40-7556-8ca7-ce5cae7f9f84" xlink:to="loc_us-gaap_InvestmentTypeCategorizationMember_019d8775-5d40-70a7-9655-f17d563b6aaf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesMember_019d8775-5d40-775a-8083-b933e788801e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_019d8775-5d40-70a7-9655-f17d563b6aaf" xlink:to="loc_us-gaap_DebtSecuritiesMember_019d8775-5d40-775a-8083-b933e788801e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeMember_019d8775-5d40-7434-99a5-2ede1dfeaebd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_019d8775-5d40-70a7-9655-f17d563b6aaf" xlink:to="loc_us-gaap_DerivativeMember_019d8775-5d40-7434-99a5-2ede1dfeaebd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MortgageReceivablesMember_019d8775-5d40-7fd8-addd-78dc94c8d062" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MortgageReceivablesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_019d8775-5d40-70a7-9655-f17d563b6aaf" xlink:to="loc_us-gaap_MortgageReceivablesMember_019d8775-5d40-7fd8-addd-78dc94c8d062" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PolicyLoansMember_019d8775-5d40-7ab5-a2be-2b33f80340ec" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PolicyLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_019d8775-5d40-70a7-9655-f17d563b6aaf" xlink:to="loc_us-gaap_PolicyLoansMember_019d8775-5d40-7ab5-a2be-2b33f80340ec" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesMember_019d8775-5d40-7084-9782-3d9663eac963" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquitySecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_019d8775-5d40-70a7-9655-f17d563b6aaf" xlink:to="loc_us-gaap_EquitySecuritiesMember_019d8775-5d40-7084-9782-3d9663eac963" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_PartnershipInterestMember_019d8775-5d40-719a-8f5b-2a2093a37154" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_PartnershipInterestMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_019d8775-5d40-70a7-9655-f17d563b6aaf" xlink:to="loc_srt_PartnershipInterestMember_019d8775-5d40-719a-8f5b-2a2093a37154" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLongTermInvestmentsMember_019d8775-5d40-7849-a788-059bbb20d58e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherLongTermInvestmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_019d8775-5d40-70a7-9655-f17d563b6aaf" xlink:to="loc_us-gaap_OtherLongTermInvestmentsMember_019d8775-5d40-7849-a788-059bbb20d58e" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermInvestmentsMember_019d8775-5d40-7009-8155-5d74e752ae16" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShortTermInvestmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_019d8775-5d40-70a7-9655-f17d563b6aaf" xlink:to="loc_us-gaap_ShortTermInvestmentsMember_019d8775-5d40-7009-8155-5d74e752ae16" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GrossInvestmentIncomeOperating_019d8775-5d40-7893-b572-da981ce5b21e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GrossInvestmentIncomeOperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_019d8775-5d40-7e27-9720-431ad962ac4c" xlink:to="loc_us-gaap_GrossInvestmentIncomeOperating_019d8775-5d40-7893-b572-da981ce5b21e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentIncomeInvestmentExpense_019d8775-5d40-758a-932e-f9e583b94b9b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentIncomeInvestmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_019d8775-5d40-7e27-9720-431ad962ac4c" xlink:to="loc_us-gaap_InvestmentIncomeInvestmentExpense_019d8775-5d40-758a-932e-f9e583b94b9b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_InvestmentIncomeOnPfaAssets_019d8775-5d40-717b-b76f-68e5246f18d1" xlink:href="unm-20260331.xsd#unm_InvestmentIncomeOnPfaAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_019d8775-5d40-7e27-9720-431ad962ac4c" xlink:to="loc_unm_InvestmentIncomeOnPfaAssets_019d8775-5d40-717b-b76f-68e5246f18d1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetInvestmentIncome_019d8775-5d40-78f9-b202-3600b57ab980" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetInvestmentIncome"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_019d8775-5d40-7e27-9720-431ad962ac4c" xlink:to="loc_us-gaap_NetInvestmentIncome_019d8775-5d40-78f9-b202-3600b57ab980" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.unum.com/role/InvestmentGainsandLossesReportedinConsolidatedStatementsofIncomeDetail" xlink:type="simple" xlink:href="unm-20260331.xsd#InvestmentGainsandLossesReportedinConsolidatedStatementsofIncomeDetail"/>
  <link:definitionLink xlink:role="http://www.unum.com/role/InvestmentGainsandLossesReportedinConsolidatedStatementsofIncomeDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfInvestmentsLineItems_019dcb14-bb72-7ae2-9677-f31b37cd910e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfInvestmentsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfInvestmentsTable_019dcb14-bb72-70f4-ba1e-b301727fb56d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfInvestmentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_019dcb14-bb72-7ae2-9677-f31b37cd910e" xlink:to="loc_us-gaap_ScheduleOfInvestmentsTable_019dcb14-bb72-70f4-ba1e-b301727fb56d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_019dcb15-103d-77d9-8a18-5b91c5bc8e26" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfInvestmentsTable_019dcb14-bb72-70f4-ba1e-b301727fb56d" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_019dcb15-103d-77d9-8a18-5b91c5bc8e26" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_019dcb15-103d-77d9-8a18-5b91c5bc8e26_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_019dcb15-103d-77d9-8a18-5b91c5bc8e26" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_019dcb15-103d-77d9-8a18-5b91c5bc8e26_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_019dcb15-103d-7af3-944a-34bfaab55432" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_019dcb15-103d-77d9-8a18-5b91c5bc8e26" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_019dcb15-103d-7af3-944a-34bfaab55432" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialRealEstateMember_019dcb15-3d5e-7e00-9683-42c6fe33e0b4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommercialRealEstateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_019dcb15-103d-7af3-944a-34bfaab55432" xlink:to="loc_us-gaap_CommercialRealEstateMember_019dcb15-3d5e-7e00-9683-42c6fe33e0b4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2_019dcb14-bb72-7a84-8321-30f893ba8d90" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_019dcb14-bb72-7ae2-9677-f31b37cd910e" xlink:to="loc_us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2_019dcb14-bb72-7a84-8321-30f893ba8d90" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.unum.com/role/InvestmentsAdditionalInformationDetail" xlink:type="simple" xlink:href="unm-20260331.xsd#InvestmentsAdditionalInformationDetail"/>
  <link:definitionLink xlink:role="http://www.unum.com/role/InvestmentsAdditionalInformationDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfInvestmentsLineItems_019d8775-5dfd-7135-914d-360e9d1a7d7c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfInvestmentsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfInvestmentsTable_019d8775-5dfd-7dc4-ba4c-c3e83dc87f1f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfInvestmentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_019d8775-5dfd-7135-914d-360e9d1a7d7c" xlink:to="loc_us-gaap_ScheduleOfInvestmentsTable_019d8775-5dfd-7dc4-ba4c-c3e83dc87f1f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ExternalCreditRatingByGroupingAxis_019d8775-5dfd-7ae3-8e9c-6acf912f35c6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ExternalCreditRatingByGroupingAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfInvestmentsTable_019d8775-5dfd-7dc4-ba4c-c3e83dc87f1f" xlink:to="loc_us-gaap_ExternalCreditRatingByGroupingAxis_019d8775-5dfd-7ae3-8e9c-6acf912f35c6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ExternalCreditRatingByGroupingDomain_019d8775-5dfd-7ae3-8e9c-6acf912f35c6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ExternalCreditRatingByGroupingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ExternalCreditRatingByGroupingAxis_019d8775-5dfd-7ae3-8e9c-6acf912f35c6" xlink:to="loc_us-gaap_ExternalCreditRatingByGroupingDomain_019d8775-5dfd-7ae3-8e9c-6acf912f35c6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ExternalCreditRatingByGroupingDomain_019d8775-5dfd-7d4f-a54c-60213dc54656" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ExternalCreditRatingByGroupingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ExternalCreditRatingByGroupingAxis_019d8775-5dfd-7ae3-8e9c-6acf912f35c6" xlink:to="loc_us-gaap_ExternalCreditRatingByGroupingDomain_019d8775-5dfd-7d4f-a54c-60213dc54656" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ExternalCreditRatingInvestmentGradeMember_019d8775-5dfd-74ae-abf7-72d659f197b1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ExternalCreditRatingInvestmentGradeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ExternalCreditRatingByGroupingDomain_019d8775-5dfd-7d4f-a54c-60213dc54656" xlink:to="loc_us-gaap_ExternalCreditRatingInvestmentGradeMember_019d8775-5dfd-74ae-abf7-72d659f197b1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ExternalCreditRatingNonInvestmentGradeMember_019d8775-5dfd-71b7-9dbb-1ce30fb23913" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ExternalCreditRatingNonInvestmentGradeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ExternalCreditRatingByGroupingDomain_019d8775-5dfd-7d4f-a54c-60213dc54656" xlink:to="loc_us-gaap_ExternalCreditRatingNonInvestmentGradeMember_019d8775-5dfd-71b7-9dbb-1ce30fb23913" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_019d8775-5dfd-769e-8d12-294c6f171748" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfInvestmentsTable_019d8775-5dfd-7dc4-ba4c-c3e83dc87f1f" xlink:to="loc_us-gaap_FinancialInstrumentAxis_019d8775-5dfd-769e-8d12-294c6f171748" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5dfd-769e-8d12-294c6f171748_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019d8775-5dfd-769e-8d12-294c6f171748" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5dfd-769e-8d12-294c6f171748_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5dfd-7211-ad1d-499d5a2a4e45" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019d8775-5dfd-769e-8d12-294c6f171748" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5dfd-7211-ad1d-499d5a2a4e45" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_PrivatePlacementFixedMaturitySecurityMember_019d8775-5dfd-7f28-9ac2-4c7a955604c0" xlink:href="unm-20260331.xsd#unm_PrivatePlacementFixedMaturitySecurityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5dfd-7211-ad1d-499d5a2a4e45" xlink:to="loc_unm_PrivatePlacementFixedMaturitySecurityMember_019d8775-5dfd-7f28-9ac2-4c7a955604c0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestmentsMember_019d8775-5dfd-7f0d-bb97-ad85f2b7b781" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityMethodInvestmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5dfd-7211-ad1d-499d5a2a4e45" xlink:to="loc_us-gaap_EquityMethodInvestmentsMember_019d8775-5dfd-7f0d-bb97-ad85f2b7b781" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019d8775-5dfd-73e7-bfd9-e525b36758ad" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfInvestmentsTable_019d8775-5dfd-7dc4-ba4c-c3e83dc87f1f" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019d8775-5dfd-73e7-bfd9-e525b36758ad" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019d8775-5dfd-73e7-bfd9-e525b36758ad_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019d8775-5dfd-73e7-bfd9-e525b36758ad" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019d8775-5dfd-73e7-bfd9-e525b36758ad_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019d8775-5dfd-756d-8bde-d987a43ba2a8" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019d8775-5dfd-73e7-bfd9-e525b36758ad" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019d8775-5dfd-756d-8bde-d987a43ba2a8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember_019d8775-5dfd-79f5-a898-3793c00a14cd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019d8775-5dfd-756d-8bde-d987a43ba2a8" xlink:to="loc_us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember_019d8775-5dfd-79f5-a898-3793c00a14cd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_019d8775-5dfd-7c31-9bd4-c846a5838f42" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfInvestmentsTable_019d8775-5dfd-7dc4-ba4c-c3e83dc87f1f" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_019d8775-5dfd-7c31-9bd4-c846a5838f42" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_019d8775-5dfd-7c31-9bd4-c846a5838f42_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_019d8775-5dfd-7c31-9bd4-c846a5838f42" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_019d8775-5dfd-7c31-9bd4-c846a5838f42_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_019d8775-5dfd-7a18-9379-7f2c56b3d99d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_019d8775-5dfd-7c31-9bd4-c846a5838f42" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_019d8775-5dfd-7a18-9379-7f2c56b3d99d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialRealEstateMember_019d8775-5dfd-70ec-bce8-b4009649c298" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommercialRealEstateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_019d8775-5dfd-7a18-9379-7f2c56b3d99d" xlink:to="loc_us-gaap_CommercialRealEstateMember_019d8775-5dfd-70ec-bce8-b4009649c298" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_UnfundedMortgageLoanCommitmentsMember_019d8775-5dfd-70ec-ac35-106a3fa1349d" xlink:href="unm-20260331.xsd#unm_UnfundedMortgageLoanCommitmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_019d8775-5dfd-7a18-9379-7f2c56b3d99d" xlink:to="loc_unm_UnfundedMortgageLoanCommitmentsMember_019d8775-5dfd-70ec-ac35-106a3fa1349d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeAxis_019d8775-5dfd-7fcb-94b7-9b9089e8a0bf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfInvestmentsTable_019d8775-5dfd-7dc4-ba4c-c3e83dc87f1f" xlink:to="loc_us-gaap_InvestmentTypeAxis_019d8775-5dfd-7fcb-94b7-9b9089e8a0bf" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeCategorizationMember_019d8775-5dfd-7fcb-94b7-9b9089e8a0bf_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentTypeCategorizationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_InvestmentTypeAxis_019d8775-5dfd-7fcb-94b7-9b9089e8a0bf" xlink:to="loc_us-gaap_InvestmentTypeCategorizationMember_019d8775-5dfd-7fcb-94b7-9b9089e8a0bf_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeCategorizationMember_019d8775-5dfd-7fd5-8e6c-67a5d98dcd26" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentTypeCategorizationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_InvestmentTypeAxis_019d8775-5dfd-7fcb-94b7-9b9089e8a0bf" xlink:to="loc_us-gaap_InvestmentTypeCategorizationMember_019d8775-5dfd-7fd5-8e6c-67a5d98dcd26" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesMember_019d8775-5dfd-7bbe-8d02-f4ee86c48ec7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquitySecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_019d8775-5dfd-7fd5-8e6c-67a5d98dcd26" xlink:to="loc_us-gaap_EquitySecuritiesMember_019d8775-5dfd-7bbe-8d02-f4ee86c48ec7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_PartnershipInterestMember_019d8775-5dfd-7a95-96e9-28ebf32c16c4" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_PartnershipInterestMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_019d8775-5dfd-7fd5-8e6c-67a5d98dcd26" xlink:to="loc_srt_PartnershipInterestMember_019d8775-5dfd-7a95-96e9-28ebf32c16c4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_019dd05b-6ab4-7b57-80e2-09365662b7d3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfInvestmentsTable_019d8775-5dfd-7dc4-ba4c-c3e83dc87f1f" xlink:to="loc_us-gaap_CreditFacilityAxis_019dd05b-6ab4-7b57-80e2-09365662b7d3" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019dd05b-6ab4-7b57-80e2-09365662b7d3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_019dd05b-6ab4-7b57-80e2-09365662b7d3" xlink:to="loc_us-gaap_CreditFacilityDomain_019dd05b-6ab4-7b57-80e2-09365662b7d3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019dd05b-6ab4-7e91-86f5-8751867035d5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_019dd05b-6ab4-7b57-80e2-09365662b7d3" xlink:to="loc_us-gaap_CreditFacilityDomain_019dd05b-6ab4-7e91-86f5-8751867035d5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_019dd05b-88ba-7fc9-96eb-6cf1f996bda5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_019dd05b-6ab4-7e91-86f5-8751867035d5" xlink:to="loc_us-gaap_LineOfCreditMember_019dd05b-88ba-7fc9-96eb-6cf1f996bda5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityAxis_019dd05b-a360-763c-aa00-a8af9e5b4e04" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfInvestmentsTable_019d8775-5dfd-7dc4-ba4c-c3e83dc87f1f" xlink:to="loc_us-gaap_LineOfCreditFacilityAxis_019dd05b-a360-763c-aa00-a8af9e5b4e04" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityLenderDomain_019dd05b-a360-763c-aa00-a8af9e5b4e04_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityLenderDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LineOfCreditFacilityAxis_019dd05b-a360-763c-aa00-a8af9e5b4e04" xlink:to="loc_us-gaap_LineOfCreditFacilityLenderDomain_019dd05b-a360-763c-aa00-a8af9e5b4e04_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityLenderDomain_019dd05b-a360-795e-ab90-61053255d3f4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityLenderDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LineOfCreditFacilityAxis_019dd05b-a360-763c-aa00-a8af9e5b4e04" xlink:to="loc_us-gaap_LineOfCreditFacilityLenderDomain_019dd05b-a360-795e-ab90-61053255d3f4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_FABLTrustMember_019dd05c-4d2a-72ef-9996-dcb344b907df" xlink:href="unm-20260331.xsd#unm_FABLTrustMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLenderDomain_019dd05b-a360-795e-ab90-61053255d3f4" xlink:to="loc_unm_FABLTrustMember_019dd05c-4d2a-72ef-9996-dcb344b907df" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionNumberOfPositions_019d8775-5dfd-71f3-9959-90ac16f80bca" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionNumberOfPositions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_019d8775-5dfd-7135-914d-360e9d1a7d7c" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionNumberOfPositions_019d8775-5dfd-71f3-9959-90ac16f80bca" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerNumberOfPositions_019d8775-5dfd-7ccc-a792-5ad6b60ee8e5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerNumberOfPositions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_019d8775-5dfd-7135-914d-360e9d1a7d7c" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerNumberOfPositions_019d8775-5dfd-7ccc-a792-5ad6b60ee8e5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueDisclosureOffbalanceSheetRisksAmountLiability_019d8775-5dfd-74ac-8a46-5e7cf4f9db15" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueDisclosureOffbalanceSheetRisksAmountLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_019d8775-5dfd-7135-914d-360e9d1a7d7c" xlink:to="loc_us-gaap_FairValueDisclosureOffbalanceSheetRisksAmountLiability_019d8775-5dfd-74ac-8a46-5e7cf4f9db15" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLongTermInvestments_019d8775-5dfd-721f-8435-a7809cd82d37" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherLongTermInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_019d8775-5dfd-7135-914d-360e9d1a7d7c" xlink:to="loc_us-gaap_OtherLongTermInvestments_019d8775-5dfd-721f-8435-a7809cd82d37" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NotesReceivableGross_019d8775-5dfd-7ca0-bbf3-da1fb96b50c4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NotesReceivableGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_019d8775-5dfd-7135-914d-360e9d1a7d7c" xlink:to="loc_us-gaap_NotesReceivableGross_019d8775-5dfd-7ca0-bbf3-da1fb96b50c4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableAllowanceForCreditLosses_019d8775-5dfd-701a-b0a2-af68ea882dd6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableAllowanceForCreditLosses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_019d8775-5dfd-7135-914d-360e9d1a7d7c" xlink:to="loc_us-gaap_FinancingReceivableAllowanceForCreditLosses_019d8775-5dfd-701a-b0a2-af68ea882dd6" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedInvestmentIncomeReceivable_019d8775-5dfd-78d8-bfc9-f47a9eaabf3e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccruedInvestmentIncomeReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_019d8775-5dfd-7135-914d-360e9d1a7d7c" xlink:to="loc_us-gaap_AccruedInvestmentIncomeReceivable_019d8775-5dfd-78d8-bfc9-f47a9eaabf3e" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing_019d8775-5dfd-7f59-9808-928a58f60fa5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_019d8775-5dfd-7135-914d-360e9d1a7d7c" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing_019d8775-5dfd-7f59-9808-928a58f60fa5" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainsLossesOnSalesOfOtherRealEstate_019d8775-5dfd-7850-bb32-b47990cecb5c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainsLossesOnSalesOfOtherRealEstate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_019d8775-5dfd-7135-914d-360e9d1a7d7c" xlink:to="loc_us-gaap_GainsLossesOnSalesOfOtherRealEstate_019d8775-5dfd-7850-bb32-b47990cecb5c" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_CommitmentsToFundCommercialMortgageLoans_019d8775-5dfd-7dd2-9cea-832f425bc5dc" xlink:href="unm-20260331.xsd#unm_CommitmentsToFundCommercialMortgageLoans"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_019d8775-5dfd-7135-914d-360e9d1a7d7c" xlink:to="loc_unm_CommitmentsToFundCommercialMortgageLoans_019d8775-5dfd-7dd2-9cea-832f425bc5dc" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsAndFinancingReceivableAllowanceForCreditLoss_019d8775-5dfd-7972-bef8-e28b2f94f025" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsAndFinancingReceivableAllowanceForCreditLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_019d8775-5dfd-7135-914d-360e9d1a7d7c" xlink:to="loc_us-gaap_AccountsAndFinancingReceivableAllowanceForCreditLoss_019d8775-5dfd-7972-bef8-e28b2f94f025" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RealEstateInvestmentPropertyNet_019d8775-5dfd-76e6-b8fc-90c19915ed0b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RealEstateInvestmentPropertyNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_019d8775-5dfd-7135-914d-360e9d1a7d7c" xlink:to="loc_us-gaap_RealEstateInvestmentPropertyNet_019d8775-5dfd-76e6-b8fc-90c19915ed0b" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RealEstateHeldforsale_019d8775-5dfd-7d37-9c47-20160a0d19ae" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RealEstateHeldforsale"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_019d8775-5dfd-7135-914d-360e9d1a7d7c" xlink:to="loc_us-gaap_RealEstateHeldforsale_019d8775-5dfd-7d37-9c47-20160a0d19ae" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RepurchaseAgreementsMaturities_019d8775-5dfd-7430-8176-6aea8d7db770" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RepurchaseAgreementsMaturities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_019d8775-5dfd-7135-914d-360e9d1a7d7c" xlink:to="loc_us-gaap_RepurchaseAgreementsMaturities_019d8775-5dfd-7430-8176-6aea8d7db770" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_CollateralRequirementsMinimumPercentageCollateralToFairValueOfSecuritiesLoanedOrPurchasedUnderRepurchaseAgreements_019d8775-5dfd-7a36-b235-5cab3deca60c" xlink:href="unm-20260331.xsd#unm_CollateralRequirementsMinimumPercentageCollateralToFairValueOfSecuritiesLoanedOrPurchasedUnderRepurchaseAgreements"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_019d8775-5dfd-7135-914d-360e9d1a7d7c" xlink:to="loc_unm_CollateralRequirementsMinimumPercentageCollateralToFairValueOfSecuritiesLoanedOrPurchasedUnderRepurchaseAgreements_019d8775-5dfd-7a36-b235-5cab3deca60c" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuritiesLoanedGross_019d8775-5dfd-7a71-8673-1846080faf4f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SecuritiesLoanedGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_019d8775-5dfd-7135-914d-360e9d1a7d7c" xlink:to="loc_us-gaap_SecuritiesLoanedGross_019d8775-5dfd-7a71-8673-1846080faf4f" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCollateralForBorrowedSecurities_019d8775-5dfd-7be6-b275-9a7d1e641192" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashCollateralForBorrowedSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_019d8775-5dfd-7135-914d-360e9d1a7d7c" xlink:to="loc_us-gaap_CashCollateralForBorrowedSecurities_019d8775-5dfd-7be6-b275-9a7d1e641192" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuritiesReceivedAsCollateral_019d8775-5dfd-77ba-95f3-4ff481844f1f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SecuritiesReceivedAsCollateral"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_019d8775-5dfd-7135-914d-360e9d1a7d7c" xlink:to="loc_us-gaap_SecuritiesReceivedAsCollateral_019d8775-5dfd-77ba-95f3-4ff481844f1f" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuritiesSoldUnderAgreementsToRepurchase_019d8775-5dfd-7109-9940-c7a903a589d9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SecuritiesSoldUnderAgreementsToRepurchase"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_019d8775-5dfd-7135-914d-360e9d1a7d7c" xlink:to="loc_us-gaap_SecuritiesSoldUnderAgreementsToRepurchase_019d8775-5dfd-7109-9940-c7a903a589d9" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnrealizedGainLossOnInvestments_019d8775-5dfd-7ae9-80d9-18d16655bcc2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UnrealizedGainLossOnInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_019d8775-5dfd-7135-914d-360e9d1a7d7c" xlink:to="loc_us-gaap_UnrealizedGainLossOnInvestments_019d8775-5dfd-7ae9-80d9-18d16655bcc2" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ManagementFeeExpense_019d8775-5dfd-7dfb-a1d7-0f53db1b5897" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ManagementFeeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_019d8775-5dfd-7135-914d-360e9d1a7d7c" xlink:to="loc_us-gaap_ManagementFeeExpense_019d8775-5dfd-7dfb-a1d7-0f53db1b5897" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableModifiedWeightedAverageTermIncreaseFromModification_019dcb17-43ae-7747-95c6-839d8999de7c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableModifiedWeightedAverageTermIncreaseFromModification"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_019d8775-5dfd-7135-914d-360e9d1a7d7c" xlink:to="loc_us-gaap_FinancingReceivableModifiedWeightedAverageTermIncreaseFromModification_019dcb17-43ae-7747-95c6-839d8999de7c" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityFairValueOfAmountOutstanding_019dd05a-c63c-7c14-926f-349c20098fc4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityFairValueOfAmountOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_019d8775-5dfd-7135-914d-360e9d1a7d7c" xlink:to="loc_us-gaap_LineOfCreditFacilityFairValueOfAmountOutstanding_019dd05a-c63c-7c14-926f-349c20098fc4" xlink:type="arc" order="22"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.unum.com/role/DerivativeFinancialInstrumentsNatureandAmountofCollateralReceivedFromandPostedToOurDerivativeCounterpartiesDetails" xlink:type="simple" xlink:href="unm-20260331.xsd#DerivativeFinancialInstrumentsNatureandAmountofCollateralReceivedFromandPostedToOurDerivativeCounterpartiesDetails"/>
  <link:definitionLink xlink:role="http://www.unum.com/role/DerivativeFinancialInstrumentsNatureandAmountofCollateralReceivedFromandPostedToOurDerivativeCounterpartiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLineItems_019d8775-5dfd-74ec-9175-2d300f4c1fef" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeTable_019d8775-5dfd-7821-81c2-788ed7eed50f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeLineItems_019d8775-5dfd-74ec-9175-2d300f4c1fef" xlink:to="loc_us-gaap_DerivativeTable_019d8775-5dfd-7821-81c2-788ed7eed50f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_019d8775-5dfd-72bf-bfea-be2ef9f1e886" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_019d8775-5dfd-7821-81c2-788ed7eed50f" xlink:to="loc_us-gaap_FinancialInstrumentAxis_019d8775-5dfd-72bf-bfea-be2ef9f1e886" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5dfd-72bf-bfea-be2ef9f1e886_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019d8775-5dfd-72bf-bfea-be2ef9f1e886" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5dfd-72bf-bfea-be2ef9f1e886_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5dfd-730c-b229-c46619657b30" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019d8775-5dfd-72bf-bfea-be2ef9f1e886" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5dfd-730c-b229-c46619657b30" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashMember_019d8775-5dfd-7540-b967-1e51d8b5b8db" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5dfd-730c-b229-c46619657b30" xlink:to="loc_us-gaap_CashMember_019d8775-5dfd-7540-b967-1e51d8b5b8db" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableforsaleSecuritiesMember_019d8775-5dfd-722e-9119-ac44bb5c90c8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableforsaleSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d8775-5dfd-730c-b229-c46619657b30" xlink:to="loc_us-gaap_AvailableforsaleSecuritiesMember_019d8775-5dfd-722e-9119-ac44bb5c90c8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeCollateralObligationToReturnCash_019d8775-5dfd-7048-af1f-ca1154055449" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeCollateralObligationToReturnCash"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019d8775-5dfd-74ec-9175-2d300f4c1fef" xlink:to="loc_us-gaap_DerivativeCollateralObligationToReturnCash_019d8775-5dfd-7048-af1f-ca1154055449" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeCollateralObligationToReturnSecurities_019d8775-5dfd-7f57-930c-fd36b83fd5ac" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeCollateralObligationToReturnSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019d8775-5dfd-74ec-9175-2d300f4c1fef" xlink:to="loc_us-gaap_DerivativeCollateralObligationToReturnSecurities_019d8775-5dfd-7f57-930c-fd36b83fd5ac" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssetNotOffsetPolicyElectionDeduction_019d8775-5dfd-7409-a961-d28dc5486e78" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeAssetNotOffsetPolicyElectionDeduction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019d8775-5dfd-74ec-9175-2d300f4c1fef" xlink:to="loc_us-gaap_DerivativeAssetNotOffsetPolicyElectionDeduction_019d8775-5dfd-7409-a961-d28dc5486e78" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeCollateralRightToReclaimCash_019d8775-5dfd-7b5a-9eeb-66e07e0c1458" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeCollateralRightToReclaimCash"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019d8775-5dfd-74ec-9175-2d300f4c1fef" xlink:to="loc_us-gaap_DerivativeCollateralRightToReclaimCash_019d8775-5dfd-7b5a-9eeb-66e07e0c1458" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeCollateralRightToReclaimSecurities_019d8775-5dfd-7c48-9d6e-ac2ca2d36547" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeCollateralRightToReclaimSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019d8775-5dfd-74ec-9175-2d300f4c1fef" xlink:to="loc_us-gaap_DerivativeCollateralRightToReclaimSecurities_019d8775-5dfd-7c48-9d6e-ac2ca2d36547" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLiabilityNotOffsetPolicyElectionDeduction_019d8775-5dfd-7263-9b7d-207a05b797a0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeLiabilityNotOffsetPolicyElectionDeduction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019d8775-5dfd-74ec-9175-2d300f4c1fef" xlink:to="loc_us-gaap_DerivativeLiabilityNotOffsetPolicyElectionDeduction_019d8775-5dfd-7263-9b7d-207a05b797a0" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.unum.com/role/DerivativeFinancialInstrumentsFairValueHedgesCarryingAmountofHedgedAssetsandCumulativeBasisAdjustmentsDetails" xlink:type="simple" xlink:href="unm-20260331.xsd#DerivativeFinancialInstrumentsFairValueHedgesCarryingAmountofHedgedAssetsandCumulativeBasisAdjustmentsDetails"/>
  <link:definitionLink xlink:role="http://www.unum.com/role/DerivativeFinancialInstrumentsFairValueHedgesCarryingAmountofHedgedAssetsandCumulativeBasisAdjustmentsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_019d8775-5dfd-797b-b388-207b97c6db58" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_019d8775-5dfd-772b-9a70-0be4beee2b59" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_019d8775-5dfd-797b-b388-207b97c6db58" xlink:to="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_019d8775-5dfd-772b-9a70-0be4beee2b59" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_InterestRateDerivativesContractTypeAxis_019d8775-5dfd-7b1e-aeb4-9baf40cfdc4b" xlink:href="unm-20260331.xsd#unm_InterestRateDerivativesContractTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_019d8775-5dfd-772b-9a70-0be4beee2b59" xlink:to="loc_unm_InterestRateDerivativesContractTypeAxis_019d8775-5dfd-7b1e-aeb4-9baf40cfdc4b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_InterestRateDerivativeContractTypeDomain_019d8775-5dfd-7b1e-aeb4-9baf40cfdc4b_default" xlink:href="unm-20260331.xsd#unm_InterestRateDerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_unm_InterestRateDerivativesContractTypeAxis_019d8775-5dfd-7b1e-aeb4-9baf40cfdc4b" xlink:to="loc_unm_InterestRateDerivativeContractTypeDomain_019d8775-5dfd-7b1e-aeb4-9baf40cfdc4b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_InterestRateDerivativeContractTypeDomain_019d8775-5dfd-7786-bb3b-bb44067fb7f5" xlink:href="unm-20260331.xsd#unm_InterestRateDerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_unm_InterestRateDerivativesContractTypeAxis_019d8775-5dfd-7b1e-aeb4-9baf40cfdc4b" xlink:to="loc_unm_InterestRateDerivativeContractTypeDomain_019d8775-5dfd-7786-bb3b-bb44067fb7f5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_DerivativeFinancialInstrumentsReceiveFixedPayFixedMember_019d8775-5dfd-7fb8-af8a-c7facc907ee6" xlink:href="unm-20260331.xsd#unm_DerivativeFinancialInstrumentsReceiveFixedPayFixedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_unm_InterestRateDerivativeContractTypeDomain_019d8775-5dfd-7786-bb3b-bb44067fb7f5" xlink:to="loc_unm_DerivativeFinancialInstrumentsReceiveFixedPayFixedMember_019d8775-5dfd-7fb8-af8a-c7facc907ee6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationAxis_019d8775-5dfd-7902-a0a9-e0df03f42e74" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_019d8775-5dfd-772b-9a70-0be4beee2b59" xlink:to="loc_us-gaap_HedgingDesignationAxis_019d8775-5dfd-7902-a0a9-e0df03f42e74" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_019d8775-5dfd-7902-a0a9-e0df03f42e74_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_HedgingDesignationAxis_019d8775-5dfd-7902-a0a9-e0df03f42e74" xlink:to="loc_us-gaap_HedgingDesignationDomain_019d8775-5dfd-7902-a0a9-e0df03f42e74_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_019d8775-5dfd-7a3e-b2a9-41bcf847322b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_HedgingDesignationAxis_019d8775-5dfd-7902-a0a9-e0df03f42e74" xlink:to="loc_us-gaap_HedgingDesignationDomain_019d8775-5dfd-7a3e-b2a9-41bcf847322b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DesignatedAsHedgingInstrumentMember_019d8775-5dfd-7467-8763-8446b0cebfa1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DesignatedAsHedgingInstrumentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingDesignationDomain_019d8775-5dfd-7a3e-b2a9-41bcf847322b" xlink:to="loc_us-gaap_DesignatedAsHedgingInstrumentMember_019d8775-5dfd-7467-8763-8446b0cebfa1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019d8775-5dfd-7d09-8411-07eefa9332ac" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_019d8775-5dfd-772b-9a70-0be4beee2b59" xlink:to="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019d8775-5dfd-7d09-8411-07eefa9332ac" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_019d8775-5dfd-7d09-8411-07eefa9332ac_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingRelationshipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019d8775-5dfd-7d09-8411-07eefa9332ac" xlink:to="loc_us-gaap_HedgingRelationshipDomain_019d8775-5dfd-7d09-8411-07eefa9332ac_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_019d8775-5dfd-7ca6-a0ae-ca5d436a27cf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingRelationshipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019d8775-5dfd-7d09-8411-07eefa9332ac" xlink:to="loc_us-gaap_HedgingRelationshipDomain_019d8775-5dfd-7ca6-a0ae-ca5d436a27cf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueHedgingMember_019d8775-5dfd-7392-87a2-7182cc10dc21" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueHedgingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingRelationshipDomain_019d8775-5dfd-7ca6-a0ae-ca5d436a27cf" xlink:to="loc_us-gaap_FairValueHedgingMember_019d8775-5dfd-7392-87a2-7182cc10dc21" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementOfFinancialPositionLocationBalanceAxis_019d8775-5dfd-7953-a532-9f9c7b593688" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementOfFinancialPositionLocationBalanceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_019d8775-5dfd-772b-9a70-0be4beee2b59" xlink:to="loc_us-gaap_StatementOfFinancialPositionLocationBalanceAxis_019d8775-5dfd-7953-a532-9f9c7b593688" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgedAssetFairValueHedgeCumulativeIncreaseDecrease_019d8775-5dfd-7c5e-81aa-34b5245c8798" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgedAssetFairValueHedgeCumulativeIncreaseDecrease"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_019d8775-5dfd-797b-b388-207b97c6db58" xlink:to="loc_us-gaap_HedgedAssetFairValueHedgeCumulativeIncreaseDecrease_019d8775-5dfd-7c5e-81aa-34b5245c8798" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgedAssetFairValueHedge_019d8775-5dfd-7d7d-b03d-e1a261cbed68" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgedAssetFairValueHedge"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_019d8775-5dfd-797b-b388-207b97c6db58" xlink:to="loc_us-gaap_HedgedAssetFairValueHedge_019d8775-5dfd-7d7d-b03d-e1a261cbed68" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgedAssetStatementOfFinancialPositionExtensibleEnumeration_019d8775-5dfd-72fa-8777-e4ff2b792c7d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgedAssetStatementOfFinancialPositionExtensibleEnumeration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_019d8775-5dfd-797b-b388-207b97c6db58" xlink:to="loc_us-gaap_HedgedAssetStatementOfFinancialPositionExtensibleEnumeration_019d8775-5dfd-72fa-8777-e4ff2b792c7d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_HedgedAssetAmortizedCost_019d8775-5dfd-74ca-8ec2-115297f9b489" xlink:href="unm-20260331.xsd#unm_HedgedAssetAmortizedCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_019d8775-5dfd-797b-b388-207b97c6db58" xlink:to="loc_unm_HedgedAssetAmortizedCost_019d8775-5dfd-74ca-8ec2-115297f9b489" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.unum.com/role/DerivativeFinancialInstrumentsFairValueHedgesCarryingAmountofHedgedAssetsandCumulativeBasisAdjustmentsDetails_1" xlink:type="simple" xlink:href="unm-20260331.xsd#DerivativeFinancialInstrumentsFairValueHedgesCarryingAmountofHedgedAssetsandCumulativeBasisAdjustmentsDetails_1"/>
  <link:definitionLink xlink:role="http://www.unum.com/role/DerivativeFinancialInstrumentsFairValueHedgesCarryingAmountofHedgedAssetsandCumulativeBasisAdjustmentsDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_019d8775-5dfd-797b-b388-207b97c6db58" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_019d8775-5dfd-772b-9a70-0be4beee2b59" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_019d8775-5dfd-797b-b388-207b97c6db58" xlink:to="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_019d8775-5dfd-772b-9a70-0be4beee2b59" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_InterestRateDerivativesContractTypeAxis_019d8775-5dfd-7b1e-aeb4-9baf40cfdc4b" xlink:href="unm-20260331.xsd#unm_InterestRateDerivativesContractTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_019d8775-5dfd-772b-9a70-0be4beee2b59" xlink:to="loc_unm_InterestRateDerivativesContractTypeAxis_019d8775-5dfd-7b1e-aeb4-9baf40cfdc4b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_InterestRateDerivativeContractTypeDomain_019d8775-5dfd-7b1e-aeb4-9baf40cfdc4b_default" xlink:href="unm-20260331.xsd#unm_InterestRateDerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_unm_InterestRateDerivativesContractTypeAxis_019d8775-5dfd-7b1e-aeb4-9baf40cfdc4b" xlink:to="loc_unm_InterestRateDerivativeContractTypeDomain_019d8775-5dfd-7b1e-aeb4-9baf40cfdc4b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_InterestRateDerivativeContractTypeDomain_019d8775-5dfd-7786-bb3b-bb44067fb7f5" xlink:href="unm-20260331.xsd#unm_InterestRateDerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_unm_InterestRateDerivativesContractTypeAxis_019d8775-5dfd-7b1e-aeb4-9baf40cfdc4b" xlink:to="loc_unm_InterestRateDerivativeContractTypeDomain_019d8775-5dfd-7786-bb3b-bb44067fb7f5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_DerivativeFinancialInstrumentsReceiveFixedPayFixedMember_019d8775-5dfd-7fb8-af8a-c7facc907ee6" xlink:href="unm-20260331.xsd#unm_DerivativeFinancialInstrumentsReceiveFixedPayFixedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_unm_InterestRateDerivativeContractTypeDomain_019d8775-5dfd-7786-bb3b-bb44067fb7f5" xlink:to="loc_unm_DerivativeFinancialInstrumentsReceiveFixedPayFixedMember_019d8775-5dfd-7fb8-af8a-c7facc907ee6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationAxis_019d8775-5dfd-7902-a0a9-e0df03f42e74" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_019d8775-5dfd-772b-9a70-0be4beee2b59" xlink:to="loc_us-gaap_HedgingDesignationAxis_019d8775-5dfd-7902-a0a9-e0df03f42e74" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_019d8775-5dfd-7902-a0a9-e0df03f42e74_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_HedgingDesignationAxis_019d8775-5dfd-7902-a0a9-e0df03f42e74" xlink:to="loc_us-gaap_HedgingDesignationDomain_019d8775-5dfd-7902-a0a9-e0df03f42e74_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_019d8775-5dfd-7a3e-b2a9-41bcf847322b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_HedgingDesignationAxis_019d8775-5dfd-7902-a0a9-e0df03f42e74" xlink:to="loc_us-gaap_HedgingDesignationDomain_019d8775-5dfd-7a3e-b2a9-41bcf847322b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DesignatedAsHedgingInstrumentMember_019d8775-5dfd-7467-8763-8446b0cebfa1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DesignatedAsHedgingInstrumentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingDesignationDomain_019d8775-5dfd-7a3e-b2a9-41bcf847322b" xlink:to="loc_us-gaap_DesignatedAsHedgingInstrumentMember_019d8775-5dfd-7467-8763-8446b0cebfa1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019d8775-5dfd-7d09-8411-07eefa9332ac" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_019d8775-5dfd-772b-9a70-0be4beee2b59" xlink:to="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019d8775-5dfd-7d09-8411-07eefa9332ac" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_019d8775-5dfd-7d09-8411-07eefa9332ac_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingRelationshipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019d8775-5dfd-7d09-8411-07eefa9332ac" xlink:to="loc_us-gaap_HedgingRelationshipDomain_019d8775-5dfd-7d09-8411-07eefa9332ac_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_019d8775-5dfd-7ca6-a0ae-ca5d436a27cf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingRelationshipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019d8775-5dfd-7d09-8411-07eefa9332ac" xlink:to="loc_us-gaap_HedgingRelationshipDomain_019d8775-5dfd-7ca6-a0ae-ca5d436a27cf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueHedgingMember_019d8775-5dfd-7392-87a2-7182cc10dc21" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueHedgingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingRelationshipDomain_019d8775-5dfd-7ca6-a0ae-ca5d436a27cf" xlink:to="loc_us-gaap_FairValueHedgingMember_019d8775-5dfd-7392-87a2-7182cc10dc21" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgedAssetFairValueHedgeCumulativeIncreaseDecrease_019d8775-5dfd-7c5e-81aa-34b5245c8798" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgedAssetFairValueHedgeCumulativeIncreaseDecrease"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_019d8775-5dfd-797b-b388-207b97c6db58" xlink:to="loc_us-gaap_HedgedAssetFairValueHedgeCumulativeIncreaseDecrease_019d8775-5dfd-7c5e-81aa-34b5245c8798" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgedAssetFairValueHedge_019d8775-5dfd-7d7d-b03d-e1a261cbed68" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgedAssetFairValueHedge"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_019d8775-5dfd-797b-b388-207b97c6db58" xlink:to="loc_us-gaap_HedgedAssetFairValueHedge_019d8775-5dfd-7d7d-b03d-e1a261cbed68" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgedAssetStatementOfFinancialPositionExtensibleEnumeration_019d8775-5dfd-72fa-8777-e4ff2b792c7d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgedAssetStatementOfFinancialPositionExtensibleEnumeration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_019d8775-5dfd-797b-b388-207b97c6db58" xlink:to="loc_us-gaap_HedgedAssetStatementOfFinancialPositionExtensibleEnumeration_019d8775-5dfd-72fa-8777-e4ff2b792c7d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_HedgedAssetAmortizedCost_019d8775-5dfd-74ca-8ec2-115297f9b489" xlink:href="unm-20260331.xsd#unm_HedgedAssetAmortizedCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_019d8775-5dfd-797b-b388-207b97c6db58" xlink:to="loc_unm_HedgedAssetAmortizedCost_019d8775-5dfd-74ca-8ec2-115297f9b489" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.unum.com/role/LocationandAmountsofDerivativeFinancialInstrumentsDetail" xlink:type="simple" xlink:href="unm-20260331.xsd#LocationandAmountsofDerivativeFinancialInstrumentsDetail"/>
  <link:definitionLink xlink:role="http://www.unum.com/role/LocationandAmountsofDerivativeFinancialInstrumentsDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLineItems_019d8775-5dfd-749a-9a7f-e606cda147ba" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable_019d8775-5dfd-7a3e-b853-40089bb9851d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeLineItems_019d8775-5dfd-749a-9a7f-e606cda147ba" xlink:to="loc_us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable_019d8775-5dfd-7a3e-b853-40089bb9851d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationAxis_019d8775-5dfd-78be-9bf0-a22d1382b2db" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable_019d8775-5dfd-7a3e-b853-40089bb9851d" xlink:to="loc_us-gaap_HedgingDesignationAxis_019d8775-5dfd-78be-9bf0-a22d1382b2db" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_019d8775-5dfd-78be-9bf0-a22d1382b2db_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_HedgingDesignationAxis_019d8775-5dfd-78be-9bf0-a22d1382b2db" xlink:to="loc_us-gaap_HedgingDesignationDomain_019d8775-5dfd-78be-9bf0-a22d1382b2db_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_019d8775-5dfd-7c0a-a0c7-d65de9f39a9f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_HedgingDesignationAxis_019d8775-5dfd-78be-9bf0-a22d1382b2db" xlink:to="loc_us-gaap_HedgingDesignationDomain_019d8775-5dfd-7c0a-a0c7-d65de9f39a9f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DesignatedAsHedgingInstrumentMember_019d8775-5dfd-7870-8bfa-b69f351780dc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DesignatedAsHedgingInstrumentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingDesignationDomain_019d8775-5dfd-7c0a-a0c7-d65de9f39a9f" xlink:to="loc_us-gaap_DesignatedAsHedgingInstrumentMember_019d8775-5dfd-7870-8bfa-b69f351780dc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NondesignatedMember_019d8775-5dfd-7cfa-8e32-fdf3a3667512" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NondesignatedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingDesignationDomain_019d8775-5dfd-7c0a-a0c7-d65de9f39a9f" xlink:to="loc_us-gaap_NondesignatedMember_019d8775-5dfd-7cfa-8e32-fdf3a3667512" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementOfFinancialPositionLocationBalanceAxis_019d8775-5dfd-7e59-9152-c07cfb65b99b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementOfFinancialPositionLocationBalanceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable_019d8775-5dfd-7a3e-b853-40089bb9851d" xlink:to="loc_us-gaap_StatementOfFinancialPositionLocationBalanceAxis_019d8775-5dfd-7e59-9152-c07cfb65b99b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_019d8775-5dfd-789d-acde-26d87da2fcfc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable_019d8775-5dfd-7a3e-b853-40089bb9851d" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_019d8775-5dfd-789d-acde-26d87da2fcfc" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-789d-acde-26d87da2fcfc_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019d8775-5dfd-789d-acde-26d87da2fcfc" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-789d-acde-26d87da2fcfc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-705d-ac70-e093bc2daef8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019d8775-5dfd-789d-acde-26d87da2fcfc" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-705d-ac70-e093bc2daef8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateSwapMember_019d8775-5dfd-7700-87ca-98bcf4758812" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestRateSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-705d-ac70-e093bc2daef8" xlink:to="loc_us-gaap_InterestRateSwapMember_019d8775-5dfd-7700-87ca-98bcf4758812" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TotalReturnSwapMember_019d8775-5dfd-7c18-8e9f-aef38ccdef79" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TotalReturnSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-705d-ac70-e093bc2daef8" xlink:to="loc_us-gaap_TotalReturnSwapMember_019d8775-5dfd-7c18-8e9f-aef38ccdef79" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmbeddedDerivativeFinancialInstrumentsMember_019d8775-5dfd-7935-aae5-71345b7a1558" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmbeddedDerivativeFinancialInstrumentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-705d-ac70-e093bc2daef8" xlink:to="loc_us-gaap_EmbeddedDerivativeFinancialInstrumentsMember_019d8775-5dfd-7935-aae5-71345b7a1558" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_ForwardBenchmarkInterestRateLockMember_019dbfbc-e3dd-74c7-9d08-3debb3864198" xlink:href="unm-20260331.xsd#unm_ForwardBenchmarkInterestRateLockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-705d-ac70-e093bc2daef8" xlink:to="loc_unm_ForwardBenchmarkInterestRateLockMember_019dbfbc-e3dd-74c7-9d08-3debb3864198" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignExchangeForwardMember_019dbfbe-1786-700c-bc27-205531edcdff" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ForeignExchangeForwardMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-705d-ac70-e093bc2daef8" xlink:to="loc_us-gaap_ForeignExchangeForwardMember_019dbfbe-1786-700c-bc27-205531edcdff" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019d8775-5dfd-72be-8d6e-ff5c2347899e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable_019d8775-5dfd-7a3e-b853-40089bb9851d" xlink:to="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019d8775-5dfd-72be-8d6e-ff5c2347899e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_019d8775-5dfd-72be-8d6e-ff5c2347899e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingRelationshipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019d8775-5dfd-72be-8d6e-ff5c2347899e" xlink:to="loc_us-gaap_HedgingRelationshipDomain_019d8775-5dfd-72be-8d6e-ff5c2347899e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_019d8775-5dfd-7c19-8caf-c01c8523ff4c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingRelationshipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019d8775-5dfd-72be-8d6e-ff5c2347899e" xlink:to="loc_us-gaap_HedgingRelationshipDomain_019d8775-5dfd-7c19-8caf-c01c8523ff4c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashFlowHedgingMember_019d8775-5dfd-78ea-aa10-3fef077ecaaf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashFlowHedgingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingRelationshipDomain_019d8775-5dfd-7c19-8caf-c01c8523ff4c" xlink:to="loc_us-gaap_CashFlowHedgingMember_019d8775-5dfd-78ea-aa10-3fef077ecaaf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueHedgingMember_019d8775-5dfd-774f-bddc-84816fed8eda" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueHedgingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingRelationshipDomain_019d8775-5dfd-7c19-8caf-c01c8523ff4c" xlink:to="loc_us-gaap_FairValueHedgingMember_019d8775-5dfd-774f-bddc-84816fed8eda" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeNotionalAmount_019d8775-5dfd-7dbc-b12c-9e71382a5f9e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeNotionalAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019d8775-5dfd-749a-9a7f-e606cda147ba" xlink:to="loc_us-gaap_DerivativeNotionalAmount_019d8775-5dfd-7dbc-b12c-9e71382a5f9e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeFairValueOfDerivativeAsset_019d8775-5dfd-72f3-811a-c5e2a55dfde7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeFairValueOfDerivativeAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019d8775-5dfd-749a-9a7f-e606cda147ba" xlink:to="loc_us-gaap_DerivativeFairValueOfDerivativeAsset_019d8775-5dfd-72f3-811a-c5e2a55dfde7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeFairValueOfDerivativeLiability_019d8775-5dfd-7527-955c-024c81f0ec1e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeFairValueOfDerivativeLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019d8775-5dfd-749a-9a7f-e606cda147ba" xlink:to="loc_us-gaap_DerivativeFairValueOfDerivativeLiability_019d8775-5dfd-7527-955c-024c81f0ec1e" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.unum.com/role/LocationandAmountsofDerivativeFinancialInstrumentsDetail_1" xlink:type="simple" xlink:href="unm-20260331.xsd#LocationandAmountsofDerivativeFinancialInstrumentsDetail_1"/>
  <link:definitionLink xlink:role="http://www.unum.com/role/LocationandAmountsofDerivativeFinancialInstrumentsDetail_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLineItems_019d8775-5dfd-749a-9a7f-e606cda147ba" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable_019d8775-5dfd-7a3e-b853-40089bb9851d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeLineItems_019d8775-5dfd-749a-9a7f-e606cda147ba" xlink:to="loc_us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable_019d8775-5dfd-7a3e-b853-40089bb9851d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationAxis_019d8775-5dfd-78be-9bf0-a22d1382b2db" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable_019d8775-5dfd-7a3e-b853-40089bb9851d" xlink:to="loc_us-gaap_HedgingDesignationAxis_019d8775-5dfd-78be-9bf0-a22d1382b2db" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_019d8775-5dfd-78be-9bf0-a22d1382b2db_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_HedgingDesignationAxis_019d8775-5dfd-78be-9bf0-a22d1382b2db" xlink:to="loc_us-gaap_HedgingDesignationDomain_019d8775-5dfd-78be-9bf0-a22d1382b2db_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_019d8775-5dfd-7c0a-a0c7-d65de9f39a9f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_HedgingDesignationAxis_019d8775-5dfd-78be-9bf0-a22d1382b2db" xlink:to="loc_us-gaap_HedgingDesignationDomain_019d8775-5dfd-7c0a-a0c7-d65de9f39a9f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DesignatedAsHedgingInstrumentMember_019d8775-5dfd-7870-8bfa-b69f351780dc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DesignatedAsHedgingInstrumentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingDesignationDomain_019d8775-5dfd-7c0a-a0c7-d65de9f39a9f" xlink:to="loc_us-gaap_DesignatedAsHedgingInstrumentMember_019d8775-5dfd-7870-8bfa-b69f351780dc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NondesignatedMember_019d8775-5dfd-7cfa-8e32-fdf3a3667512" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NondesignatedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingDesignationDomain_019d8775-5dfd-7c0a-a0c7-d65de9f39a9f" xlink:to="loc_us-gaap_NondesignatedMember_019d8775-5dfd-7cfa-8e32-fdf3a3667512" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_019d8775-5dfd-789d-acde-26d87da2fcfc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable_019d8775-5dfd-7a3e-b853-40089bb9851d" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_019d8775-5dfd-789d-acde-26d87da2fcfc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-789d-acde-26d87da2fcfc_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019d8775-5dfd-789d-acde-26d87da2fcfc" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-789d-acde-26d87da2fcfc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-705d-ac70-e093bc2daef8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019d8775-5dfd-789d-acde-26d87da2fcfc" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-705d-ac70-e093bc2daef8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateSwapMember_019d8775-5dfd-7700-87ca-98bcf4758812" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestRateSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-705d-ac70-e093bc2daef8" xlink:to="loc_us-gaap_InterestRateSwapMember_019d8775-5dfd-7700-87ca-98bcf4758812" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TotalReturnSwapMember_019d8775-5dfd-7c18-8e9f-aef38ccdef79" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TotalReturnSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-705d-ac70-e093bc2daef8" xlink:to="loc_us-gaap_TotalReturnSwapMember_019d8775-5dfd-7c18-8e9f-aef38ccdef79" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmbeddedDerivativeFinancialInstrumentsMember_019d8775-5dfd-7935-aae5-71345b7a1558" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmbeddedDerivativeFinancialInstrumentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-705d-ac70-e093bc2daef8" xlink:to="loc_us-gaap_EmbeddedDerivativeFinancialInstrumentsMember_019d8775-5dfd-7935-aae5-71345b7a1558" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_ForwardBenchmarkInterestRateLockMember_019dbfbc-e3dd-74c7-9d08-3debb3864198" xlink:href="unm-20260331.xsd#unm_ForwardBenchmarkInterestRateLockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-705d-ac70-e093bc2daef8" xlink:to="loc_unm_ForwardBenchmarkInterestRateLockMember_019dbfbc-e3dd-74c7-9d08-3debb3864198" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignExchangeForwardMember_019dbfbe-1786-700c-bc27-205531edcdff" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ForeignExchangeForwardMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-705d-ac70-e093bc2daef8" xlink:to="loc_us-gaap_ForeignExchangeForwardMember_019dbfbe-1786-700c-bc27-205531edcdff" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019d8775-5dfd-72be-8d6e-ff5c2347899e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable_019d8775-5dfd-7a3e-b853-40089bb9851d" xlink:to="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019d8775-5dfd-72be-8d6e-ff5c2347899e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_019d8775-5dfd-72be-8d6e-ff5c2347899e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingRelationshipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019d8775-5dfd-72be-8d6e-ff5c2347899e" xlink:to="loc_us-gaap_HedgingRelationshipDomain_019d8775-5dfd-72be-8d6e-ff5c2347899e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_019d8775-5dfd-7c19-8caf-c01c8523ff4c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingRelationshipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019d8775-5dfd-72be-8d6e-ff5c2347899e" xlink:to="loc_us-gaap_HedgingRelationshipDomain_019d8775-5dfd-7c19-8caf-c01c8523ff4c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashFlowHedgingMember_019d8775-5dfd-78ea-aa10-3fef077ecaaf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashFlowHedgingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingRelationshipDomain_019d8775-5dfd-7c19-8caf-c01c8523ff4c" xlink:to="loc_us-gaap_CashFlowHedgingMember_019d8775-5dfd-78ea-aa10-3fef077ecaaf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueHedgingMember_019d8775-5dfd-774f-bddc-84816fed8eda" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueHedgingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingRelationshipDomain_019d8775-5dfd-7c19-8caf-c01c8523ff4c" xlink:to="loc_us-gaap_FairValueHedgingMember_019d8775-5dfd-774f-bddc-84816fed8eda" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeNotionalAmount_019d8775-5dfd-7dbc-b12c-9e71382a5f9e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeNotionalAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019d8775-5dfd-749a-9a7f-e606cda147ba" xlink:to="loc_us-gaap_DerivativeNotionalAmount_019d8775-5dfd-7dbc-b12c-9e71382a5f9e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeFairValueOfDerivativeAsset_019d8775-5dfd-72f3-811a-c5e2a55dfde7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeFairValueOfDerivativeAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019d8775-5dfd-749a-9a7f-e606cda147ba" xlink:to="loc_us-gaap_DerivativeFairValueOfDerivativeAsset_019d8775-5dfd-72f3-811a-c5e2a55dfde7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeFairValueOfDerivativeLiability_019d8775-5dfd-7527-955c-024c81f0ec1e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeFairValueOfDerivativeLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019d8775-5dfd-749a-9a7f-e606cda147ba" xlink:to="loc_us-gaap_DerivativeFairValueOfDerivativeLiability_019d8775-5dfd-7527-955c-024c81f0ec1e" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.unum.com/role/DerivativeFinancialInstrumentsLocationofGainsandLossesDesignatedasHedgingInstrumentsConsolidatedStatementsofIncomeDetails" xlink:type="simple" xlink:href="unm-20260331.xsd#DerivativeFinancialInstrumentsLocationofGainsandLossesDesignatedasHedgingInstrumentsConsolidatedStatementsofIncomeDetails"/>
  <link:definitionLink xlink:role="http://www.unum.com/role/DerivativeFinancialInstrumentsLocationofGainsandLossesDesignatedasHedgingInstrumentsConsolidatedStatementsofIncomeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_019d8775-5dfd-702a-a951-ec67bcedb98c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentsGainLossLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_019d8775-5dfd-7fc2-8b7c-22fd63e75591" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_019d8775-5dfd-702a-a951-ec67bcedb98c" xlink:to="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_019d8775-5dfd-7fc2-8b7c-22fd63e75591" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationAxis_019d8775-5dfd-7972-a143-b2e4595abb3a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_019d8775-5dfd-7fc2-8b7c-22fd63e75591" xlink:to="loc_us-gaap_HedgingDesignationAxis_019d8775-5dfd-7972-a143-b2e4595abb3a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_019d8775-5dfd-7972-a143-b2e4595abb3a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_HedgingDesignationAxis_019d8775-5dfd-7972-a143-b2e4595abb3a" xlink:to="loc_us-gaap_HedgingDesignationDomain_019d8775-5dfd-7972-a143-b2e4595abb3a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_019d8775-5dfd-7ce2-bd4d-1c0143a0d5ff" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_HedgingDesignationAxis_019d8775-5dfd-7972-a143-b2e4595abb3a" xlink:to="loc_us-gaap_HedgingDesignationDomain_019d8775-5dfd-7ce2-bd4d-1c0143a0d5ff" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DesignatedAsHedgingInstrumentMember_019d8775-5dfd-7362-b51e-26bc2c6a57d6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DesignatedAsHedgingInstrumentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingDesignationDomain_019d8775-5dfd-7ce2-bd4d-1c0143a0d5ff" xlink:to="loc_us-gaap_DesignatedAsHedgingInstrumentMember_019d8775-5dfd-7362-b51e-26bc2c6a57d6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_019d8775-5dfd-7a03-9d70-2e3caf9030bd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_019d8775-5dfd-7fc2-8b7c-22fd63e75591" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_019d8775-5dfd-7a03-9d70-2e3caf9030bd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-7a03-9d70-2e3caf9030bd_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019d8775-5dfd-7a03-9d70-2e3caf9030bd" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-7a03-9d70-2e3caf9030bd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-72f8-ba21-490e194e4404" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019d8775-5dfd-7a03-9d70-2e3caf9030bd" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-72f8-ba21-490e194e4404" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateSwapMember_019d8775-5dfd-7dd4-9066-02266db922ec" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestRateSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-72f8-ba21-490e194e4404" xlink:to="loc_us-gaap_InterestRateSwapMember_019d8775-5dfd-7dd4-9066-02266db922ec" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignExchangeContractMember_019d8775-5dfd-7679-a6f8-ebc878121942" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ForeignExchangeContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-72f8-ba21-490e194e4404" xlink:to="loc_us-gaap_ForeignExchangeContractMember_019d8775-5dfd-7679-a6f8-ebc878121942" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_ForwardBenchmarkInterestRateLockMember_019dbfc2-8e6f-7d22-8546-3562592091e9" xlink:href="unm-20260331.xsd#unm_ForwardBenchmarkInterestRateLockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-72f8-ba21-490e194e4404" xlink:to="loc_unm_ForwardBenchmarkInterestRateLockMember_019dbfc2-8e6f-7d22-8546-3562592091e9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_019d8775-5dfd-7646-8861-b3f635c49d72" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementOfIncomeLocationBalanceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_019d8775-5dfd-7fc2-8b7c-22fd63e75591" xlink:to="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_019d8775-5dfd-7646-8861-b3f635c49d72" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019d8775-5dfd-7507-8d80-e5327a29ebda" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_019d8775-5dfd-7fc2-8b7c-22fd63e75591" xlink:to="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019d8775-5dfd-7507-8d80-e5327a29ebda" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_019d8775-5dfd-7507-8d80-e5327a29ebda_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingRelationshipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019d8775-5dfd-7507-8d80-e5327a29ebda" xlink:to="loc_us-gaap_HedgingRelationshipDomain_019d8775-5dfd-7507-8d80-e5327a29ebda_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_019d8775-5dfd-7d32-9752-a7a3fea45999" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingRelationshipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019d8775-5dfd-7507-8d80-e5327a29ebda" xlink:to="loc_us-gaap_HedgingRelationshipDomain_019d8775-5dfd-7d32-9752-a7a3fea45999" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashFlowHedgingMember_019d8775-5dfd-7344-960b-d66dd8dcf709" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashFlowHedgingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingRelationshipDomain_019d8775-5dfd-7d32-9752-a7a3fea45999" xlink:to="loc_us-gaap_CashFlowHedgingMember_019d8775-5dfd-7344-960b-d66dd8dcf709" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueHedgingMember_019d8775-5dfd-79d9-aba6-8f1d4b79c4d9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueHedgingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingRelationshipDomain_019d8775-5dfd-7d32-9752-a7a3fea45999" xlink:to="loc_us-gaap_FairValueHedgingMember_019d8775-5dfd-79d9-aba6-8f1d4b79c4d9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetInvestmentIncome_019d8775-5dfd-7006-b9b1-23d45138e42f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetInvestmentIncome"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_019d8775-5dfd-702a-a951-ec67bcedb98c" xlink:to="loc_us-gaap_NetInvestmentIncome_019d8775-5dfd-7006-b9b1-23d45138e42f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnInvestments_019d8775-5dfd-766e-b2da-2713cf445def" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainLossOnInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_019d8775-5dfd-702a-a951-ec67bcedb98c" xlink:to="loc_us-gaap_GainLossOnInvestments_019d8775-5dfd-766e-b2da-2713cf445def" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestAndDebtExpense_019d8775-5dfd-746a-bb5f-b62453299936" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestAndDebtExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_019d8775-5dfd-702a-a951-ec67bcedb98c" xlink:to="loc_us-gaap_InterestAndDebtExpense_019d8775-5dfd-746a-bb5f-b62453299936" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeGainLossOnDerivativeNet_019d8775-5dfd-7b4b-a3f6-1efe5a40f806" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeGainLossOnDerivativeNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_019d8775-5dfd-702a-a951-ec67bcedb98c" xlink:to="loc_us-gaap_DerivativeGainLossOnDerivativeNet_019d8775-5dfd-7b4b-a3f6-1efe5a40f806" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.unum.com/role/DerivativeFinancialInstrumentsLocationofGainsandLossesDesignatedasHedgingInstrumentsConsolidatedStatementsofIncomeDetails_1" xlink:type="simple" xlink:href="unm-20260331.xsd#DerivativeFinancialInstrumentsLocationofGainsandLossesDesignatedasHedgingInstrumentsConsolidatedStatementsofIncomeDetails_1"/>
  <link:definitionLink xlink:role="http://www.unum.com/role/DerivativeFinancialInstrumentsLocationofGainsandLossesDesignatedasHedgingInstrumentsConsolidatedStatementsofIncomeDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_019d8775-5dfd-702a-a951-ec67bcedb98c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentsGainLossLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_019d8775-5dfd-7fc2-8b7c-22fd63e75591" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_019d8775-5dfd-702a-a951-ec67bcedb98c" xlink:to="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_019d8775-5dfd-7fc2-8b7c-22fd63e75591" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationAxis_019d8775-5dfd-7972-a143-b2e4595abb3a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_019d8775-5dfd-7fc2-8b7c-22fd63e75591" xlink:to="loc_us-gaap_HedgingDesignationAxis_019d8775-5dfd-7972-a143-b2e4595abb3a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_019d8775-5dfd-7972-a143-b2e4595abb3a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_HedgingDesignationAxis_019d8775-5dfd-7972-a143-b2e4595abb3a" xlink:to="loc_us-gaap_HedgingDesignationDomain_019d8775-5dfd-7972-a143-b2e4595abb3a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_019d8775-5dfd-7ce2-bd4d-1c0143a0d5ff" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_HedgingDesignationAxis_019d8775-5dfd-7972-a143-b2e4595abb3a" xlink:to="loc_us-gaap_HedgingDesignationDomain_019d8775-5dfd-7ce2-bd4d-1c0143a0d5ff" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DesignatedAsHedgingInstrumentMember_019d8775-5dfd-7362-b51e-26bc2c6a57d6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DesignatedAsHedgingInstrumentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingDesignationDomain_019d8775-5dfd-7ce2-bd4d-1c0143a0d5ff" xlink:to="loc_us-gaap_DesignatedAsHedgingInstrumentMember_019d8775-5dfd-7362-b51e-26bc2c6a57d6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_019d8775-5dfd-7a03-9d70-2e3caf9030bd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_019d8775-5dfd-7fc2-8b7c-22fd63e75591" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_019d8775-5dfd-7a03-9d70-2e3caf9030bd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-7a03-9d70-2e3caf9030bd_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019d8775-5dfd-7a03-9d70-2e3caf9030bd" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-7a03-9d70-2e3caf9030bd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-72f8-ba21-490e194e4404" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019d8775-5dfd-7a03-9d70-2e3caf9030bd" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-72f8-ba21-490e194e4404" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateSwapMember_019d8775-5dfd-7dd4-9066-02266db922ec" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestRateSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-72f8-ba21-490e194e4404" xlink:to="loc_us-gaap_InterestRateSwapMember_019d8775-5dfd-7dd4-9066-02266db922ec" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignExchangeContractMember_019d8775-5dfd-7679-a6f8-ebc878121942" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ForeignExchangeContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-72f8-ba21-490e194e4404" xlink:to="loc_us-gaap_ForeignExchangeContractMember_019d8775-5dfd-7679-a6f8-ebc878121942" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_ForwardBenchmarkInterestRateLockMember_019dbfc2-8e6f-7d22-8546-3562592091e9" xlink:href="unm-20260331.xsd#unm_ForwardBenchmarkInterestRateLockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-72f8-ba21-490e194e4404" xlink:to="loc_unm_ForwardBenchmarkInterestRateLockMember_019dbfc2-8e6f-7d22-8546-3562592091e9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019d8775-5dfd-7507-8d80-e5327a29ebda" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_019d8775-5dfd-7fc2-8b7c-22fd63e75591" xlink:to="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019d8775-5dfd-7507-8d80-e5327a29ebda" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_019d8775-5dfd-7507-8d80-e5327a29ebda_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingRelationshipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019d8775-5dfd-7507-8d80-e5327a29ebda" xlink:to="loc_us-gaap_HedgingRelationshipDomain_019d8775-5dfd-7507-8d80-e5327a29ebda_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_019d8775-5dfd-7d32-9752-a7a3fea45999" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingRelationshipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019d8775-5dfd-7507-8d80-e5327a29ebda" xlink:to="loc_us-gaap_HedgingRelationshipDomain_019d8775-5dfd-7d32-9752-a7a3fea45999" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashFlowHedgingMember_019d8775-5dfd-7344-960b-d66dd8dcf709" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashFlowHedgingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingRelationshipDomain_019d8775-5dfd-7d32-9752-a7a3fea45999" xlink:to="loc_us-gaap_CashFlowHedgingMember_019d8775-5dfd-7344-960b-d66dd8dcf709" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueHedgingMember_019d8775-5dfd-79d9-aba6-8f1d4b79c4d9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueHedgingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingRelationshipDomain_019d8775-5dfd-7d32-9752-a7a3fea45999" xlink:to="loc_us-gaap_FairValueHedgingMember_019d8775-5dfd-79d9-aba6-8f1d4b79c4d9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetInvestmentIncome_019d8775-5dfd-7006-b9b1-23d45138e42f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetInvestmentIncome"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_019d8775-5dfd-702a-a951-ec67bcedb98c" xlink:to="loc_us-gaap_NetInvestmentIncome_019d8775-5dfd-7006-b9b1-23d45138e42f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnInvestments_019d8775-5dfd-766e-b2da-2713cf445def" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainLossOnInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_019d8775-5dfd-702a-a951-ec67bcedb98c" xlink:to="loc_us-gaap_GainLossOnInvestments_019d8775-5dfd-766e-b2da-2713cf445def" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestAndDebtExpense_019d8775-5dfd-746a-bb5f-b62453299936" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestAndDebtExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_019d8775-5dfd-702a-a951-ec67bcedb98c" xlink:to="loc_us-gaap_InterestAndDebtExpense_019d8775-5dfd-746a-bb5f-b62453299936" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeGainLossOnDerivativeNet_019d8775-5dfd-7b4b-a3f6-1efe5a40f806" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeGainLossOnDerivativeNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_019d8775-5dfd-702a-a951-ec67bcedb98c" xlink:to="loc_us-gaap_DerivativeGainLossOnDerivativeNet_019d8775-5dfd-7b4b-a3f6-1efe5a40f806" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.unum.com/role/LocationofGainsandLossesonDerivativeInstrumentsDesignatedasCashFlowHedgingInstrumentsDetail" xlink:type="simple" xlink:href="unm-20260331.xsd#LocationofGainsandLossesonDerivativeInstrumentsDesignatedasCashFlowHedgingInstrumentsDetail"/>
  <link:definitionLink xlink:role="http://www.unum.com/role/LocationofGainsandLossesonDerivativeInstrumentsDesignatedasCashFlowHedgingInstrumentsDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_019d8775-5dfd-73da-bcf3-523fbf5fcbd9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentsGainLossLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_019d8775-5dfd-76ab-a590-dadf6e30514c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_019d8775-5dfd-73da-bcf3-523fbf5fcbd9" xlink:to="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_019d8775-5dfd-76ab-a590-dadf6e30514c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_019d8775-5dfd-77a7-b960-22997f5c5b38" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_019d8775-5dfd-76ab-a590-dadf6e30514c" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_019d8775-5dfd-77a7-b960-22997f5c5b38" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-77a7-b960-22997f5c5b38_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019d8775-5dfd-77a7-b960-22997f5c5b38" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-77a7-b960-22997f5c5b38_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-7ace-9899-4a1bbed75c0a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019d8775-5dfd-77a7-b960-22997f5c5b38" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-7ace-9899-4a1bbed75c0a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_ForwardBenchmarkInterestRateLockMember_019d8775-5dfd-75a8-83cc-e7ad724eeca5" xlink:href="unm-20260331.xsd#unm_ForwardBenchmarkInterestRateLockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-7ace-9899-4a1bbed75c0a" xlink:to="loc_unm_ForwardBenchmarkInterestRateLockMember_019d8775-5dfd-75a8-83cc-e7ad724eeca5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignExchangeContractMember_019d8775-5dfd-7696-bfec-c56ff8a4526a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ForeignExchangeContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-7ace-9899-4a1bbed75c0a" xlink:to="loc_us-gaap_ForeignExchangeContractMember_019d8775-5dfd-7696-bfec-c56ff8a4526a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationAxis_019d8775-5dfd-7c2f-acd0-3a24a28288eb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_019d8775-5dfd-76ab-a590-dadf6e30514c" xlink:to="loc_us-gaap_HedgingDesignationAxis_019d8775-5dfd-7c2f-acd0-3a24a28288eb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_019d8775-5dfd-7c2f-acd0-3a24a28288eb_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_HedgingDesignationAxis_019d8775-5dfd-7c2f-acd0-3a24a28288eb" xlink:to="loc_us-gaap_HedgingDesignationDomain_019d8775-5dfd-7c2f-acd0-3a24a28288eb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_019d8775-5dfd-7bee-b930-87cd7facb016" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_HedgingDesignationAxis_019d8775-5dfd-7c2f-acd0-3a24a28288eb" xlink:to="loc_us-gaap_HedgingDesignationDomain_019d8775-5dfd-7bee-b930-87cd7facb016" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DesignatedAsHedgingInstrumentMember_019d8775-5dfd-77fd-9e57-6a4dcd7886b2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DesignatedAsHedgingInstrumentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingDesignationDomain_019d8775-5dfd-7bee-b930-87cd7facb016" xlink:to="loc_us-gaap_DesignatedAsHedgingInstrumentMember_019d8775-5dfd-77fd-9e57-6a4dcd7886b2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019d8775-5dfd-70b4-ba7a-204f93746ce3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_019d8775-5dfd-76ab-a590-dadf6e30514c" xlink:to="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019d8775-5dfd-70b4-ba7a-204f93746ce3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_019d8775-5dfd-70b4-ba7a-204f93746ce3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingRelationshipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019d8775-5dfd-70b4-ba7a-204f93746ce3" xlink:to="loc_us-gaap_HedgingRelationshipDomain_019d8775-5dfd-70b4-ba7a-204f93746ce3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_019d8775-5dfd-733b-b9fb-26ed809c64f4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingRelationshipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019d8775-5dfd-70b4-ba7a-204f93746ce3" xlink:to="loc_us-gaap_HedgingRelationshipDomain_019d8775-5dfd-733b-b9fb-26ed809c64f4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashFlowHedgingMember_019d8775-5dfd-7a54-9ba1-b57ac108d78e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashFlowHedgingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingRelationshipDomain_019d8775-5dfd-733b-b9fb-26ed809c64f4" xlink:to="loc_us-gaap_CashFlowHedgingMember_019d8775-5dfd-7a54-9ba1-b57ac108d78e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossBeforeReclassificationAndTax_019d8775-5dfd-7fe4-8d94-cb8256e6732a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossBeforeReclassificationAndTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_019d8775-5dfd-73da-bcf3-523fbf5fcbd9" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossBeforeReclassificationAndTax_019d8775-5dfd-7fe4-8d94-cb8256e6732a" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.unum.com/role/GainsandLossesonDerivativesNotDesignatedasHedgingInstrumentsDetail" xlink:type="simple" xlink:href="unm-20260331.xsd#GainsandLossesonDerivativesNotDesignatedasHedgingInstrumentsDetail"/>
  <link:definitionLink xlink:role="http://www.unum.com/role/GainsandLossesonDerivativesNotDesignatedasHedgingInstrumentsDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_019d8775-5dfd-726f-9783-2bad229a9591" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentsGainLossLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_019d8775-5dfd-7f82-be18-75ef2a94b9d4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_019d8775-5dfd-726f-9783-2bad229a9591" xlink:to="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_019d8775-5dfd-7f82-be18-75ef2a94b9d4" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_019d8775-5dfd-769b-9f09-8ba5d97d0558" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_019d8775-5dfd-7f82-be18-75ef2a94b9d4" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_019d8775-5dfd-769b-9f09-8ba5d97d0558" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-769b-9f09-8ba5d97d0558_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019d8775-5dfd-769b-9f09-8ba5d97d0558" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-769b-9f09-8ba5d97d0558_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-7a0c-870f-783800ba6477" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019d8775-5dfd-769b-9f09-8ba5d97d0558" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-7a0c-870f-783800ba6477" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignExchangeContractMember_019d8775-5dfd-78ce-8001-1c64f5f993f5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ForeignExchangeContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-7a0c-870f-783800ba6477" xlink:to="loc_us-gaap_ForeignExchangeContractMember_019d8775-5dfd-78ce-8001-1c64f5f993f5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmbeddedDerivativeFinancialInstrumentsMember_019d8775-5dfd-796a-ba06-0a5ffff1f63e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmbeddedDerivativeFinancialInstrumentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-7a0c-870f-783800ba6477" xlink:to="loc_us-gaap_EmbeddedDerivativeFinancialInstrumentsMember_019d8775-5dfd-796a-ba06-0a5ffff1f63e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TotalReturnSwapMember_019d8775-5dfd-7302-add3-2bbf40962d07" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TotalReturnSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-7a0c-870f-783800ba6477" xlink:to="loc_us-gaap_TotalReturnSwapMember_019d8775-5dfd-7302-add3-2bbf40962d07" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationAxis_019d8775-5dfd-7e53-afaf-5eb65a7dfbb6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_019d8775-5dfd-7f82-be18-75ef2a94b9d4" xlink:to="loc_us-gaap_HedgingDesignationAxis_019d8775-5dfd-7e53-afaf-5eb65a7dfbb6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_019d8775-5dfd-7e53-afaf-5eb65a7dfbb6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_HedgingDesignationAxis_019d8775-5dfd-7e53-afaf-5eb65a7dfbb6" xlink:to="loc_us-gaap_HedgingDesignationDomain_019d8775-5dfd-7e53-afaf-5eb65a7dfbb6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_019d8775-5dfd-7c20-9c2e-ff4b1c5495ce" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_HedgingDesignationAxis_019d8775-5dfd-7e53-afaf-5eb65a7dfbb6" xlink:to="loc_us-gaap_HedgingDesignationDomain_019d8775-5dfd-7c20-9c2e-ff4b1c5495ce" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NondesignatedMember_019d8775-5dfd-70c1-b735-db3b3415305f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NondesignatedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingDesignationDomain_019d8775-5dfd-7c20-9c2e-ff4b1c5495ce" xlink:to="loc_us-gaap_NondesignatedMember_019d8775-5dfd-70c1-b735-db3b3415305f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_019d8775-5dfd-7a07-b26d-63c410e605fc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementOfIncomeLocationBalanceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_019d8775-5dfd-7f82-be18-75ef2a94b9d4" xlink:to="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_019d8775-5dfd-7a07-b26d-63c410e605fc" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeGainLossOnDerivativeNet_019d8775-5dfd-7f25-a113-df9564a53359" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeGainLossOnDerivativeNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_019d8775-5dfd-726f-9783-2bad229a9591" xlink:to="loc_us-gaap_DerivativeGainLossOnDerivativeNet_019d8775-5dfd-7f25-a113-df9564a53359" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.unum.com/role/GainsandLossesonDerivativesNotDesignatedasHedgingInstrumentsDetail_1" xlink:type="simple" xlink:href="unm-20260331.xsd#GainsandLossesonDerivativesNotDesignatedasHedgingInstrumentsDetail_1"/>
  <link:definitionLink xlink:role="http://www.unum.com/role/GainsandLossesonDerivativesNotDesignatedasHedgingInstrumentsDetail_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_019d8775-5dfd-726f-9783-2bad229a9591" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentsGainLossLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_019d8775-5dfd-7f82-be18-75ef2a94b9d4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_019d8775-5dfd-726f-9783-2bad229a9591" xlink:to="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_019d8775-5dfd-7f82-be18-75ef2a94b9d4" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_019d8775-5dfd-769b-9f09-8ba5d97d0558" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_019d8775-5dfd-7f82-be18-75ef2a94b9d4" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_019d8775-5dfd-769b-9f09-8ba5d97d0558" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-769b-9f09-8ba5d97d0558_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019d8775-5dfd-769b-9f09-8ba5d97d0558" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-769b-9f09-8ba5d97d0558_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-7a0c-870f-783800ba6477" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019d8775-5dfd-769b-9f09-8ba5d97d0558" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-7a0c-870f-783800ba6477" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignExchangeContractMember_019d8775-5dfd-78ce-8001-1c64f5f993f5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ForeignExchangeContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-7a0c-870f-783800ba6477" xlink:to="loc_us-gaap_ForeignExchangeContractMember_019d8775-5dfd-78ce-8001-1c64f5f993f5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmbeddedDerivativeFinancialInstrumentsMember_019d8775-5dfd-796a-ba06-0a5ffff1f63e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmbeddedDerivativeFinancialInstrumentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-7a0c-870f-783800ba6477" xlink:to="loc_us-gaap_EmbeddedDerivativeFinancialInstrumentsMember_019d8775-5dfd-796a-ba06-0a5ffff1f63e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TotalReturnSwapMember_019d8775-5dfd-7302-add3-2bbf40962d07" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TotalReturnSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-7a0c-870f-783800ba6477" xlink:to="loc_us-gaap_TotalReturnSwapMember_019d8775-5dfd-7302-add3-2bbf40962d07" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationAxis_019d8775-5dfd-7e53-afaf-5eb65a7dfbb6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_019d8775-5dfd-7f82-be18-75ef2a94b9d4" xlink:to="loc_us-gaap_HedgingDesignationAxis_019d8775-5dfd-7e53-afaf-5eb65a7dfbb6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_019d8775-5dfd-7e53-afaf-5eb65a7dfbb6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_HedgingDesignationAxis_019d8775-5dfd-7e53-afaf-5eb65a7dfbb6" xlink:to="loc_us-gaap_HedgingDesignationDomain_019d8775-5dfd-7e53-afaf-5eb65a7dfbb6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_019d8775-5dfd-7c20-9c2e-ff4b1c5495ce" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_HedgingDesignationAxis_019d8775-5dfd-7e53-afaf-5eb65a7dfbb6" xlink:to="loc_us-gaap_HedgingDesignationDomain_019d8775-5dfd-7c20-9c2e-ff4b1c5495ce" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NondesignatedMember_019d8775-5dfd-70c1-b735-db3b3415305f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NondesignatedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingDesignationDomain_019d8775-5dfd-7c20-9c2e-ff4b1c5495ce" xlink:to="loc_us-gaap_NondesignatedMember_019d8775-5dfd-70c1-b735-db3b3415305f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeGainLossOnDerivativeNet_019d8775-5dfd-7f25-a113-df9564a53359" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeGainLossOnDerivativeNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_019d8775-5dfd-726f-9783-2bad229a9591" xlink:to="loc_us-gaap_DerivativeGainLossOnDerivativeNet_019d8775-5dfd-7f25-a113-df9564a53359" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.unum.com/role/DerivativeFinancialInstrumentsAdditionalInformationDetail" xlink:type="simple" xlink:href="unm-20260331.xsd#DerivativeFinancialInstrumentsAdditionalInformationDetail"/>
  <link:definitionLink xlink:role="http://www.unum.com/role/DerivativeFinancialInstrumentsAdditionalInformationDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLineItems_019d8775-5dfd-7a13-8811-4c327782c9e8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeTable_019d8775-5dfd-79ad-be04-1d269a6eb238" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeLineItems_019d8775-5dfd-7a13-8811-4c327782c9e8" xlink:to="loc_us-gaap_DerivativeTable_019d8775-5dfd-79ad-be04-1d269a6eb238" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_CreditExposureAxis_019d8775-5dfd-7976-984f-caffa2c0ef84" xlink:href="unm-20260331.xsd#unm_CreditExposureAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_019d8775-5dfd-79ad-be04-1d269a6eb238" xlink:to="loc_unm_CreditExposureAxis_019d8775-5dfd-7976-984f-caffa2c0ef84" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_CreditExposureDomain_019d8775-5dfd-7976-984f-caffa2c0ef84_default" xlink:href="unm-20260331.xsd#unm_CreditExposureDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_unm_CreditExposureAxis_019d8775-5dfd-7976-984f-caffa2c0ef84" xlink:to="loc_unm_CreditExposureDomain_019d8775-5dfd-7976-984f-caffa2c0ef84_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_CreditExposureDomain_019d8775-5dfd-7058-8cec-e380d2eb61fd" xlink:href="unm-20260331.xsd#unm_CreditExposureDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_unm_CreditExposureAxis_019d8775-5dfd-7976-984f-caffa2c0ef84" xlink:to="loc_unm_CreditExposureDomain_019d8775-5dfd-7058-8cec-e380d2eb61fd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_CreditExposureMember_019d8775-5dfd-7436-bdc6-ed526ebcfca7" xlink:href="unm-20260331.xsd#unm_CreditExposureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_unm_CreditExposureDomain_019d8775-5dfd-7058-8cec-e380d2eb61fd" xlink:to="loc_unm_CreditExposureMember_019d8775-5dfd-7436-bdc6-ed526ebcfca7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_InterestRateDerivativesContractTypeAxis_019d8775-5dfd-764a-a03f-89a0f37a4034" xlink:href="unm-20260331.xsd#unm_InterestRateDerivativesContractTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_019d8775-5dfd-79ad-be04-1d269a6eb238" xlink:to="loc_unm_InterestRateDerivativesContractTypeAxis_019d8775-5dfd-764a-a03f-89a0f37a4034" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_InterestRateDerivativeContractTypeDomain_019d8775-5dfd-764a-a03f-89a0f37a4034_default" xlink:href="unm-20260331.xsd#unm_InterestRateDerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_unm_InterestRateDerivativesContractTypeAxis_019d8775-5dfd-764a-a03f-89a0f37a4034" xlink:to="loc_unm_InterestRateDerivativeContractTypeDomain_019d8775-5dfd-764a-a03f-89a0f37a4034_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_InterestRateDerivativeContractTypeDomain_019d8775-5dfd-7138-8247-c8441faad770" xlink:href="unm-20260331.xsd#unm_InterestRateDerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_unm_InterestRateDerivativesContractTypeAxis_019d8775-5dfd-764a-a03f-89a0f37a4034" xlink:to="loc_unm_InterestRateDerivativeContractTypeDomain_019d8775-5dfd-7138-8247-c8441faad770" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_DerivativeFinancialInstrumentsReceiveFixedPayFixedMember_019d8775-5dfd-7f7e-b302-112e748c69b0" xlink:href="unm-20260331.xsd#unm_DerivativeFinancialInstrumentsReceiveFixedPayFixedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_unm_InterestRateDerivativeContractTypeDomain_019d8775-5dfd-7138-8247-c8441faad770" xlink:to="loc_unm_DerivativeFinancialInstrumentsReceiveFixedPayFixedMember_019d8775-5dfd-7f7e-b302-112e748c69b0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_019d8775-5dfd-7ffb-b76a-a76bcc18fb0d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_019d8775-5dfd-79ad-be04-1d269a6eb238" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_019d8775-5dfd-7ffb-b76a-a76bcc18fb0d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-7ffb-b76a-a76bcc18fb0d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019d8775-5dfd-7ffb-b76a-a76bcc18fb0d" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-7ffb-b76a-a76bcc18fb0d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-7fa2-9106-474d5aaca399" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019d8775-5dfd-7ffb-b76a-a76bcc18fb0d" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-7fa2-9106-474d5aaca399" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateSwapMember_019d8775-5dfd-7cd1-a502-03aaf113195b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestRateSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-7fa2-9106-474d5aaca399" xlink:to="loc_us-gaap_InterestRateSwapMember_019d8775-5dfd-7cd1-a502-03aaf113195b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TotalReturnSwapMember_019d8775-5dfd-705a-a27c-f6c6e702d816" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TotalReturnSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-7fa2-9106-474d5aaca399" xlink:to="loc_us-gaap_TotalReturnSwapMember_019d8775-5dfd-705a-a27c-f6c6e702d816" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_ForwardBenchmarkInterestRateLockMember_019dbfbe-b17b-7601-a4fb-7e935d748287" xlink:href="unm-20260331.xsd#unm_ForwardBenchmarkInterestRateLockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-7fa2-9106-474d5aaca399" xlink:to="loc_unm_ForwardBenchmarkInterestRateLockMember_019dbfbe-b17b-7601-a4fb-7e935d748287" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignExchangeForwardMember_019dbfbf-728a-7a49-abdc-33bf63685163" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ForeignExchangeForwardMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-7fa2-9106-474d5aaca399" xlink:to="loc_us-gaap_ForeignExchangeForwardMember_019dbfbf-728a-7a49-abdc-33bf63685163" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019d8775-5dfd-77c8-8032-3aae01b0f3b5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_019d8775-5dfd-79ad-be04-1d269a6eb238" xlink:to="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019d8775-5dfd-77c8-8032-3aae01b0f3b5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_019d8775-5dfd-77c8-8032-3aae01b0f3b5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingRelationshipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019d8775-5dfd-77c8-8032-3aae01b0f3b5" xlink:to="loc_us-gaap_HedgingRelationshipDomain_019d8775-5dfd-77c8-8032-3aae01b0f3b5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_019d8775-5dfd-7558-9258-7113b870f70a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingRelationshipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019d8775-5dfd-77c8-8032-3aae01b0f3b5" xlink:to="loc_us-gaap_HedgingRelationshipDomain_019d8775-5dfd-7558-9258-7113b870f70a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashFlowHedgingMember_019d8775-5dfd-713d-9fa6-2d7ed8ef299c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashFlowHedgingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingRelationshipDomain_019d8775-5dfd-7558-9258-7113b870f70a" xlink:to="loc_us-gaap_CashFlowHedgingMember_019d8775-5dfd-713d-9fa6-2d7ed8ef299c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueHedgingMember_019d8775-5dfd-7c19-8d21-1f01f7d97242" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueHedgingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingRelationshipDomain_019d8775-5dfd-7558-9258-7113b870f70a" xlink:to="loc_us-gaap_FairValueHedgingMember_019d8775-5dfd-7c19-8d21-1f01f7d97242" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationAxis_019d8775-5dfd-7412-8a9d-9456a4540f99" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_019d8775-5dfd-79ad-be04-1d269a6eb238" xlink:to="loc_us-gaap_HedgingDesignationAxis_019d8775-5dfd-7412-8a9d-9456a4540f99" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_019d8775-5dfd-7412-8a9d-9456a4540f99_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_HedgingDesignationAxis_019d8775-5dfd-7412-8a9d-9456a4540f99" xlink:to="loc_us-gaap_HedgingDesignationDomain_019d8775-5dfd-7412-8a9d-9456a4540f99_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_019d8775-5dfd-7cc4-99b4-8121ea13d744" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_HedgingDesignationAxis_019d8775-5dfd-7412-8a9d-9456a4540f99" xlink:to="loc_us-gaap_HedgingDesignationDomain_019d8775-5dfd-7cc4-99b4-8121ea13d744" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DesignatedAsHedgingInstrumentMember_019d8775-5dfd-7723-99cf-ac8a9b983f07" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DesignatedAsHedgingInstrumentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingDesignationDomain_019d8775-5dfd-7cc4-99b4-8121ea13d744" xlink:to="loc_us-gaap_DesignatedAsHedgingInstrumentMember_019d8775-5dfd-7723-99cf-ac8a9b983f07" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NondesignatedMember_019d8775-5dfd-7409-8501-0c3c9419e943" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NondesignatedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingDesignationDomain_019d8775-5dfd-7cc4-99b4-8121ea13d744" xlink:to="loc_us-gaap_NondesignatedMember_019d8775-5dfd-7409-8501-0c3c9419e943" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_019d8775-5dfd-7f94-bffd-0049bb9a4a43" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementOfIncomeLocationBalanceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_019d8775-5dfd-79ad-be04-1d269a6eb238" xlink:to="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_019d8775-5dfd-7f94-bffd-0049bb9a4a43" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_DerivativePurposeAxis_019d8775-5dfd-7bf0-a932-1e83728b0c34" xlink:href="unm-20260331.xsd#unm_DerivativePurposeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_019d8775-5dfd-79ad-be04-1d269a6eb238" xlink:to="loc_unm_DerivativePurposeAxis_019d8775-5dfd-7bf0-a932-1e83728b0c34" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_DerivativePurposeDomain_019d8775-5dfd-7bf0-a932-1e83728b0c34_default" xlink:href="unm-20260331.xsd#unm_DerivativePurposeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_unm_DerivativePurposeAxis_019d8775-5dfd-7bf0-a932-1e83728b0c34" xlink:to="loc_unm_DerivativePurposeDomain_019d8775-5dfd-7bf0-a932-1e83728b0c34_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_DerivativePurposeDomain_019d8775-5dfd-7aeb-9047-45a6f5bf3777" xlink:href="unm-20260331.xsd#unm_DerivativePurposeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_unm_DerivativePurposeAxis_019d8775-5dfd-7bf0-a932-1e83728b0c34" xlink:to="loc_unm_DerivativePurposeDomain_019d8775-5dfd-7aeb-9047-45a6f5bf3777" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_FairValueVolatilityMember_019d8775-5dfd-7c07-abda-fc4a33a0c489" xlink:href="unm-20260331.xsd#unm_FairValueVolatilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_unm_DerivativePurposeDomain_019d8775-5dfd-7aeb-9047-45a6f5bf3777" xlink:to="loc_unm_FairValueVolatilityMember_019d8775-5dfd-7c07-abda-fc4a33a0c489" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_CreditSpreadsAndInterestRateVolatilityMember_019d8775-5dfd-745f-a968-1e84214e67f1" xlink:href="unm-20260331.xsd#unm_CreditSpreadsAndInterestRateVolatilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_unm_DerivativePurposeDomain_019d8775-5dfd-7aeb-9047-45a6f5bf3777" xlink:to="loc_unm_CreditSpreadsAndInterestRateVolatilityMember_019d8775-5dfd-745f-a968-1e84214e67f1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueConcentrationOfRiskDerivativeFinancialInstrumentsAssets_019d8775-5dfd-7953-a201-67b006310513" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueConcentrationOfRiskDerivativeFinancialInstrumentsAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019d8775-5dfd-7a13-8811-4c327782c9e8" xlink:to="loc_us-gaap_FairValueConcentrationOfRiskDerivativeFinancialInstrumentsAssets_019d8775-5dfd-7953-a201-67b006310513" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeNetLiabilityPositionAggregateFairValue_019d8775-5dfd-78ee-95e1-6dbe501f54a8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeNetLiabilityPositionAggregateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019d8775-5dfd-7a13-8811-4c327782c9e8" xlink:to="loc_us-gaap_DerivativeNetLiabilityPositionAggregateFairValue_019d8775-5dfd-78ee-95e1-6dbe501f54a8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeNotionalAmount_019d8775-5dfd-7fe2-b223-e68ff518c763" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeNotionalAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019d8775-5dfd-7a13-8811-4c327782c9e8" xlink:to="loc_us-gaap_DerivativeNotionalAmount_019d8775-5dfd-7fe2-b223-e68ff518c763" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashFlowHedgeGainLossToBeReclassifiedWithinTwelveMonths_019d8775-5dfd-7a13-afec-d83fd1f2c79b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashFlowHedgeGainLossToBeReclassifiedWithinTwelveMonths"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019d8775-5dfd-7a13-8811-4c327782c9e8" xlink:to="loc_us-gaap_CashFlowHedgeGainLossToBeReclassifiedWithinTwelveMonths_019d8775-5dfd-7a13-afec-d83fd1f2c79b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossFromComponentsExcludedFromAssessmentOfFairValueHedgeEffectivenessNet_019d8775-5dfd-75a1-b830-4d9127429c52" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainLossFromComponentsExcludedFromAssessmentOfFairValueHedgeEffectivenessNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019d8775-5dfd-7a13-8811-4c327782c9e8" xlink:to="loc_us-gaap_GainLossFromComponentsExcludedFromAssessmentOfFairValueHedgeEffectivenessNet_019d8775-5dfd-75a1-b830-4d9127429c52" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossFromHedgedFirmCommitmentNotQualifyingAsFairValueHedgeNet_019d8775-5dfd-7ddd-a3ac-671aa871e0b8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainLossFromHedgedFirmCommitmentNotQualifyingAsFairValueHedgeNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019d8775-5dfd-7a13-8811-4c327782c9e8" xlink:to="loc_us-gaap_GainLossFromHedgedFirmCommitmentNotQualifyingAsFairValueHedgeNet_019d8775-5dfd-7ddd-a3ac-671aa871e0b8" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MaximumLengthOfTimeHedgedInCashFlowHedge1_019d8775-5dfd-79b8-ad71-e18988c70f10" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MaximumLengthOfTimeHedgedInCashFlowHedge1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019d8775-5dfd-7a13-8811-4c327782c9e8" xlink:to="loc_us-gaap_MaximumLengthOfTimeHedgedInCashFlowHedge1_019d8775-5dfd-79b8-ad71-e18988c70f10" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.unum.com/role/DerivativeFinancialInstrumentsAdditionalInformationDetail_1" xlink:type="simple" xlink:href="unm-20260331.xsd#DerivativeFinancialInstrumentsAdditionalInformationDetail_1"/>
  <link:definitionLink xlink:role="http://www.unum.com/role/DerivativeFinancialInstrumentsAdditionalInformationDetail_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLineItems_019d8775-5dfd-7a13-8811-4c327782c9e8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeTable_019d8775-5dfd-79ad-be04-1d269a6eb238" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeLineItems_019d8775-5dfd-7a13-8811-4c327782c9e8" xlink:to="loc_us-gaap_DerivativeTable_019d8775-5dfd-79ad-be04-1d269a6eb238" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_CreditExposureAxis_019d8775-5dfd-7976-984f-caffa2c0ef84" xlink:href="unm-20260331.xsd#unm_CreditExposureAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_019d8775-5dfd-79ad-be04-1d269a6eb238" xlink:to="loc_unm_CreditExposureAxis_019d8775-5dfd-7976-984f-caffa2c0ef84" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_CreditExposureDomain_019d8775-5dfd-7976-984f-caffa2c0ef84_default" xlink:href="unm-20260331.xsd#unm_CreditExposureDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_unm_CreditExposureAxis_019d8775-5dfd-7976-984f-caffa2c0ef84" xlink:to="loc_unm_CreditExposureDomain_019d8775-5dfd-7976-984f-caffa2c0ef84_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_CreditExposureDomain_019d8775-5dfd-7058-8cec-e380d2eb61fd" xlink:href="unm-20260331.xsd#unm_CreditExposureDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_unm_CreditExposureAxis_019d8775-5dfd-7976-984f-caffa2c0ef84" xlink:to="loc_unm_CreditExposureDomain_019d8775-5dfd-7058-8cec-e380d2eb61fd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_CreditExposureMember_019d8775-5dfd-7436-bdc6-ed526ebcfca7" xlink:href="unm-20260331.xsd#unm_CreditExposureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_unm_CreditExposureDomain_019d8775-5dfd-7058-8cec-e380d2eb61fd" xlink:to="loc_unm_CreditExposureMember_019d8775-5dfd-7436-bdc6-ed526ebcfca7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_InterestRateDerivativesContractTypeAxis_019d8775-5dfd-764a-a03f-89a0f37a4034" xlink:href="unm-20260331.xsd#unm_InterestRateDerivativesContractTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_019d8775-5dfd-79ad-be04-1d269a6eb238" xlink:to="loc_unm_InterestRateDerivativesContractTypeAxis_019d8775-5dfd-764a-a03f-89a0f37a4034" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_InterestRateDerivativeContractTypeDomain_019d8775-5dfd-764a-a03f-89a0f37a4034_default" xlink:href="unm-20260331.xsd#unm_InterestRateDerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_unm_InterestRateDerivativesContractTypeAxis_019d8775-5dfd-764a-a03f-89a0f37a4034" xlink:to="loc_unm_InterestRateDerivativeContractTypeDomain_019d8775-5dfd-764a-a03f-89a0f37a4034_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_InterestRateDerivativeContractTypeDomain_019d8775-5dfd-7138-8247-c8441faad770" xlink:href="unm-20260331.xsd#unm_InterestRateDerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_unm_InterestRateDerivativesContractTypeAxis_019d8775-5dfd-764a-a03f-89a0f37a4034" xlink:to="loc_unm_InterestRateDerivativeContractTypeDomain_019d8775-5dfd-7138-8247-c8441faad770" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_DerivativeFinancialInstrumentsReceiveFixedPayFixedMember_019d8775-5dfd-7f7e-b302-112e748c69b0" xlink:href="unm-20260331.xsd#unm_DerivativeFinancialInstrumentsReceiveFixedPayFixedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_unm_InterestRateDerivativeContractTypeDomain_019d8775-5dfd-7138-8247-c8441faad770" xlink:to="loc_unm_DerivativeFinancialInstrumentsReceiveFixedPayFixedMember_019d8775-5dfd-7f7e-b302-112e748c69b0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_019d8775-5dfd-7ffb-b76a-a76bcc18fb0d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_019d8775-5dfd-79ad-be04-1d269a6eb238" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_019d8775-5dfd-7ffb-b76a-a76bcc18fb0d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-7ffb-b76a-a76bcc18fb0d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019d8775-5dfd-7ffb-b76a-a76bcc18fb0d" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-7ffb-b76a-a76bcc18fb0d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-7fa2-9106-474d5aaca399" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019d8775-5dfd-7ffb-b76a-a76bcc18fb0d" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-7fa2-9106-474d5aaca399" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateSwapMember_019d8775-5dfd-7cd1-a502-03aaf113195b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestRateSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-7fa2-9106-474d5aaca399" xlink:to="loc_us-gaap_InterestRateSwapMember_019d8775-5dfd-7cd1-a502-03aaf113195b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TotalReturnSwapMember_019d8775-5dfd-705a-a27c-f6c6e702d816" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TotalReturnSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-7fa2-9106-474d5aaca399" xlink:to="loc_us-gaap_TotalReturnSwapMember_019d8775-5dfd-705a-a27c-f6c6e702d816" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_ForwardBenchmarkInterestRateLockMember_019dbfbe-b17b-7601-a4fb-7e935d748287" xlink:href="unm-20260331.xsd#unm_ForwardBenchmarkInterestRateLockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-7fa2-9106-474d5aaca399" xlink:to="loc_unm_ForwardBenchmarkInterestRateLockMember_019dbfbe-b17b-7601-a4fb-7e935d748287" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignExchangeForwardMember_019dbfbf-728a-7a49-abdc-33bf63685163" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ForeignExchangeForwardMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-7fa2-9106-474d5aaca399" xlink:to="loc_us-gaap_ForeignExchangeForwardMember_019dbfbf-728a-7a49-abdc-33bf63685163" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019d8775-5dfd-77c8-8032-3aae01b0f3b5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_019d8775-5dfd-79ad-be04-1d269a6eb238" xlink:to="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019d8775-5dfd-77c8-8032-3aae01b0f3b5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_019d8775-5dfd-77c8-8032-3aae01b0f3b5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingRelationshipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019d8775-5dfd-77c8-8032-3aae01b0f3b5" xlink:to="loc_us-gaap_HedgingRelationshipDomain_019d8775-5dfd-77c8-8032-3aae01b0f3b5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_019d8775-5dfd-7558-9258-7113b870f70a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingRelationshipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019d8775-5dfd-77c8-8032-3aae01b0f3b5" xlink:to="loc_us-gaap_HedgingRelationshipDomain_019d8775-5dfd-7558-9258-7113b870f70a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashFlowHedgingMember_019d8775-5dfd-713d-9fa6-2d7ed8ef299c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashFlowHedgingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingRelationshipDomain_019d8775-5dfd-7558-9258-7113b870f70a" xlink:to="loc_us-gaap_CashFlowHedgingMember_019d8775-5dfd-713d-9fa6-2d7ed8ef299c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueHedgingMember_019d8775-5dfd-7c19-8d21-1f01f7d97242" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueHedgingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingRelationshipDomain_019d8775-5dfd-7558-9258-7113b870f70a" xlink:to="loc_us-gaap_FairValueHedgingMember_019d8775-5dfd-7c19-8d21-1f01f7d97242" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationAxis_019d8775-5dfd-7412-8a9d-9456a4540f99" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_019d8775-5dfd-79ad-be04-1d269a6eb238" xlink:to="loc_us-gaap_HedgingDesignationAxis_019d8775-5dfd-7412-8a9d-9456a4540f99" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_019d8775-5dfd-7412-8a9d-9456a4540f99_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_HedgingDesignationAxis_019d8775-5dfd-7412-8a9d-9456a4540f99" xlink:to="loc_us-gaap_HedgingDesignationDomain_019d8775-5dfd-7412-8a9d-9456a4540f99_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_019d8775-5dfd-7cc4-99b4-8121ea13d744" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_HedgingDesignationAxis_019d8775-5dfd-7412-8a9d-9456a4540f99" xlink:to="loc_us-gaap_HedgingDesignationDomain_019d8775-5dfd-7cc4-99b4-8121ea13d744" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DesignatedAsHedgingInstrumentMember_019d8775-5dfd-7723-99cf-ac8a9b983f07" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DesignatedAsHedgingInstrumentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingDesignationDomain_019d8775-5dfd-7cc4-99b4-8121ea13d744" xlink:to="loc_us-gaap_DesignatedAsHedgingInstrumentMember_019d8775-5dfd-7723-99cf-ac8a9b983f07" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NondesignatedMember_019d8775-5dfd-7409-8501-0c3c9419e943" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NondesignatedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingDesignationDomain_019d8775-5dfd-7cc4-99b4-8121ea13d744" xlink:to="loc_us-gaap_NondesignatedMember_019d8775-5dfd-7409-8501-0c3c9419e943" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_DerivativePurposeAxis_019d8775-5dfd-7bf0-a932-1e83728b0c34" xlink:href="unm-20260331.xsd#unm_DerivativePurposeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_019d8775-5dfd-79ad-be04-1d269a6eb238" xlink:to="loc_unm_DerivativePurposeAxis_019d8775-5dfd-7bf0-a932-1e83728b0c34" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_DerivativePurposeDomain_019d8775-5dfd-7bf0-a932-1e83728b0c34_default" xlink:href="unm-20260331.xsd#unm_DerivativePurposeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_unm_DerivativePurposeAxis_019d8775-5dfd-7bf0-a932-1e83728b0c34" xlink:to="loc_unm_DerivativePurposeDomain_019d8775-5dfd-7bf0-a932-1e83728b0c34_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_DerivativePurposeDomain_019d8775-5dfd-7aeb-9047-45a6f5bf3777" xlink:href="unm-20260331.xsd#unm_DerivativePurposeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_unm_DerivativePurposeAxis_019d8775-5dfd-7bf0-a932-1e83728b0c34" xlink:to="loc_unm_DerivativePurposeDomain_019d8775-5dfd-7aeb-9047-45a6f5bf3777" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_FairValueVolatilityMember_019d8775-5dfd-7c07-abda-fc4a33a0c489" xlink:href="unm-20260331.xsd#unm_FairValueVolatilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_unm_DerivativePurposeDomain_019d8775-5dfd-7aeb-9047-45a6f5bf3777" xlink:to="loc_unm_FairValueVolatilityMember_019d8775-5dfd-7c07-abda-fc4a33a0c489" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_CreditSpreadsAndInterestRateVolatilityMember_019d8775-5dfd-745f-a968-1e84214e67f1" xlink:href="unm-20260331.xsd#unm_CreditSpreadsAndInterestRateVolatilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_unm_DerivativePurposeDomain_019d8775-5dfd-7aeb-9047-45a6f5bf3777" xlink:to="loc_unm_CreditSpreadsAndInterestRateVolatilityMember_019d8775-5dfd-745f-a968-1e84214e67f1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueConcentrationOfRiskDerivativeFinancialInstrumentsAssets_019d8775-5dfd-7953-a201-67b006310513" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueConcentrationOfRiskDerivativeFinancialInstrumentsAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019d8775-5dfd-7a13-8811-4c327782c9e8" xlink:to="loc_us-gaap_FairValueConcentrationOfRiskDerivativeFinancialInstrumentsAssets_019d8775-5dfd-7953-a201-67b006310513" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeNetLiabilityPositionAggregateFairValue_019d8775-5dfd-78ee-95e1-6dbe501f54a8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeNetLiabilityPositionAggregateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019d8775-5dfd-7a13-8811-4c327782c9e8" xlink:to="loc_us-gaap_DerivativeNetLiabilityPositionAggregateFairValue_019d8775-5dfd-78ee-95e1-6dbe501f54a8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeNotionalAmount_019d8775-5dfd-7fe2-b223-e68ff518c763" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeNotionalAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019d8775-5dfd-7a13-8811-4c327782c9e8" xlink:to="loc_us-gaap_DerivativeNotionalAmount_019d8775-5dfd-7fe2-b223-e68ff518c763" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashFlowHedgeGainLossToBeReclassifiedWithinTwelveMonths_019d8775-5dfd-7a13-afec-d83fd1f2c79b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashFlowHedgeGainLossToBeReclassifiedWithinTwelveMonths"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019d8775-5dfd-7a13-8811-4c327782c9e8" xlink:to="loc_us-gaap_CashFlowHedgeGainLossToBeReclassifiedWithinTwelveMonths_019d8775-5dfd-7a13-afec-d83fd1f2c79b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossFromComponentsExcludedFromAssessmentOfFairValueHedgeEffectivenessNet_019d8775-5dfd-75a1-b830-4d9127429c52" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainLossFromComponentsExcludedFromAssessmentOfFairValueHedgeEffectivenessNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019d8775-5dfd-7a13-8811-4c327782c9e8" xlink:to="loc_us-gaap_GainLossFromComponentsExcludedFromAssessmentOfFairValueHedgeEffectivenessNet_019d8775-5dfd-75a1-b830-4d9127429c52" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossFromHedgedFirmCommitmentNotQualifyingAsFairValueHedgeNet_019d8775-5dfd-7ddd-a3ac-671aa871e0b8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainLossFromHedgedFirmCommitmentNotQualifyingAsFairValueHedgeNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019d8775-5dfd-7a13-8811-4c327782c9e8" xlink:to="loc_us-gaap_GainLossFromHedgedFirmCommitmentNotQualifyingAsFairValueHedgeNet_019d8775-5dfd-7ddd-a3ac-671aa871e0b8" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MaximumLengthOfTimeHedgedInCashFlowHedge1_019d8775-5dfd-79b8-ad71-e18988c70f10" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MaximumLengthOfTimeHedgedInCashFlowHedge1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019d8775-5dfd-7a13-8811-4c327782c9e8" xlink:to="loc_us-gaap_MaximumLengthOfTimeHedgedInCashFlowHedge1_019d8775-5dfd-79b8-ad71-e18988c70f10" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.unum.com/role/ScheduleofAccumulatedOtherComprehensiveIncomeLossDetails" xlink:type="simple" xlink:href="unm-20260331.xsd#ScheduleofAccumulatedOtherComprehensiveIncomeLossDetails"/>
  <link:definitionLink xlink:role="http://www.unum.com/role/ScheduleofAccumulatedOtherComprehensiveIncomeLossDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_019d8775-5dfd-7815-a60a-35d74c473a83" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_019d8775-5dfd-7dbe-bc78-13c41ede7b4b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_019d8775-5dfd-7815-a60a-35d74c473a83" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_019d8775-5dfd-7dbe-bc78-13c41ede7b4b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019d8775-5dfd-7fb3-8bdf-73f43265ba6b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_019d8775-5dfd-7dbe-bc78-13c41ede7b4b" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019d8775-5dfd-7fb3-8bdf-73f43265ba6b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019d8775-5dfd-7fb3-8bdf-73f43265ba6b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019d8775-5dfd-7fb3-8bdf-73f43265ba6b" xlink:to="loc_us-gaap_EquityComponentDomain_019d8775-5dfd-7fb3-8bdf-73f43265ba6b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019d8775-5dfd-7a18-a215-78b5ab74f27e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019d8775-5dfd-7fb3-8bdf-73f43265ba6b" xlink:to="loc_us-gaap_EquityComponentDomain_019d8775-5dfd-7a18-a215-78b5ab74f27e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember_019d8775-5dfd-7461-9b9f-a99c985b8a54" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019d8775-5dfd-7a18-a215-78b5ab74f27e" xlink:to="loc_us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember_019d8775-5dfd-7461-9b9f-a99c985b8a54" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AociLiabilityForFuturePolicyBenefitParentMember_019d8775-5dfd-7390-9407-ed9dc31532f6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AociLiabilityForFuturePolicyBenefitParentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019d8775-5dfd-7a18-a215-78b5ab74f27e" xlink:to="loc_us-gaap_AociLiabilityForFuturePolicyBenefitParentMember_019d8775-5dfd-7390-9407-ed9dc31532f6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedGainLossNetCashFlowHedgeParentMember_019d8775-5dfd-7d39-ab38-30d9d3f7e3cb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedGainLossNetCashFlowHedgeParentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019d8775-5dfd-7a18-a215-78b5ab74f27e" xlink:to="loc_us-gaap_AccumulatedGainLossNetCashFlowHedgeParentMember_019d8775-5dfd-7d39-ab38-30d9d3f7e3cb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedTranslationAdjustmentMember_019d8775-5dfd-7de1-89f1-ed5e98a3990d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedTranslationAdjustmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019d8775-5dfd-7a18-a215-78b5ab74f27e" xlink:to="loc_us-gaap_AccumulatedTranslationAdjustmentMember_019d8775-5dfd-7de1-89f1-ed5e98a3990d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember_019d8775-5dfd-7c02-b405-52c4ed142eb2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019d8775-5dfd-7a18-a215-78b5ab74f27e" xlink:to="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember_019d8775-5dfd-7c02-b405-52c4ed142eb2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_019d8775-5dfd-7b2f-aa47-912cba671ac1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_019d8775-5dfd-7815-a60a-35d74c473a83" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_019d8775-5dfd-7b2f-aa47-912cba671ac1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax_019d8775-5dfd-74e4-adfc-44acdf82281e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_019d8775-5dfd-7815-a60a-35d74c473a83" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax_019d8775-5dfd-74e4-adfc-44acdf82281e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax_019d8775-5dfd-7113-b47f-68fbd5687231" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_019d8775-5dfd-7815-a60a-35d74c473a83" xlink:to="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax_019d8775-5dfd-7113-b47f-68fbd5687231" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_019d8775-5dfd-74e6-bf61-1113b4ff9f7f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_019d8775-5dfd-7815-a60a-35d74c473a83" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_019d8775-5dfd-74e6-bf61-1113b4ff9f7f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_019d8775-5dfd-7ae4-b583-c3cd6b43495e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.unum.com/role/ScheduleofReclassificationsOutofAccumulatedOtherComprehensiveIncomeLossDetails" xlink:type="simple" xlink:href="unm-20260331.xsd#ScheduleofReclassificationsOutofAccumulatedOtherComprehensiveIncomeLossDetails"/>
  <link:definitionLink xlink:role="http://www.unum.com/role/ScheduleofReclassificationsOutofAccumulatedOtherComprehensiveIncomeLossDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems_019d8775-5dfd-743e-a8d5-2620f860f525" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeTable_019d8775-5dfd-736f-b5b6-0737395fb0ee" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems_019d8775-5dfd-743e-a8d5-2620f860f525" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeTable_019d8775-5dfd-736f-b5b6-0737395fb0ee" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_019d8775-5dfd-7e08-9ed0-9e2bbbe5cc8f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeTable_019d8775-5dfd-736f-b5b6-0737395fb0ee" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_019d8775-5dfd-7e08-9ed0-9e2bbbe5cc8f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_019d8775-5dfd-7e08-9ed0-9e2bbbe5cc8f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_019d8775-5dfd-7e08-9ed0-9e2bbbe5cc8f" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_019d8775-5dfd-7e08-9ed0-9e2bbbe5cc8f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_019d8775-5dfd-7505-9c73-de046cecbbcf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_019d8775-5dfd-7e08-9ed0-9e2bbbe5cc8f" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_019d8775-5dfd-7505-9c73-de046cecbbcf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember_019d8775-5dfd-7785-874f-2175c200561d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_019d8775-5dfd-7505-9c73-de046cecbbcf" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember_019d8775-5dfd-7785-874f-2175c200561d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019d8775-5dfd-79f6-81af-9d0ac9ebd488" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeTable_019d8775-5dfd-736f-b5b6-0737395fb0ee" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019d8775-5dfd-79f6-81af-9d0ac9ebd488" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019d8775-5dfd-79f6-81af-9d0ac9ebd488_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019d8775-5dfd-79f6-81af-9d0ac9ebd488" xlink:to="loc_us-gaap_EquityComponentDomain_019d8775-5dfd-79f6-81af-9d0ac9ebd488_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019d8775-5dfd-750b-9258-a18cffd08ab6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019d8775-5dfd-79f6-81af-9d0ac9ebd488" xlink:to="loc_us-gaap_EquityComponentDomain_019d8775-5dfd-750b-9258-a18cffd08ab6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember_019d8775-5dfd-7184-b297-9cb6246d7f61" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019d8775-5dfd-750b-9258-a18cffd08ab6" xlink:to="loc_us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember_019d8775-5dfd-7184-b297-9cb6246d7f61" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedGainLossNetCashFlowHedgeParentMember_019d8775-5dfd-7787-9210-f16d6c094883" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedGainLossNetCashFlowHedgeParentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019d8775-5dfd-750b-9258-a18cffd08ab6" xlink:to="loc_us-gaap_AccumulatedGainLossNetCashFlowHedgeParentMember_019d8775-5dfd-7787-9210-f16d6c094883" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentNetUnamortizedGainLossMember_019d8775-5dfd-73c3-9129-307fa63f4a85" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedDefinedBenefitPlansAdjustmentNetUnamortizedGainLossMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019d8775-5dfd-750b-9258-a18cffd08ab6" xlink:to="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentNetUnamortizedGainLossMember_019d8775-5dfd-73c3-9129-307fa63f4a85" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentNetPriorServiceCostCreditMember_019d8775-5dfd-7994-8eca-77e4e43dac05" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedDefinedBenefitPlansAdjustmentNetPriorServiceCostCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019d8775-5dfd-750b-9258-a18cffd08ab6" xlink:to="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentNetPriorServiceCostCreditMember_019d8775-5dfd-7994-8eca-77e4e43dac05" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember_019d8775-5dfd-7420-8458-16b478ce0ce6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019d8775-5dfd-750b-9258-a18cffd08ab6" xlink:to="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember_019d8775-5dfd-7420-8458-16b478ce0ce6" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_019d8775-5dfd-7b8e-a247-7a435357fbdb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeTable_019d8775-5dfd-736f-b5b6-0737395fb0ee" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_019d8775-5dfd-7b8e-a247-7a435357fbdb" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-7b8e-a247-7a435357fbdb_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019d8775-5dfd-7b8e-a247-7a435357fbdb" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-7b8e-a247-7a435357fbdb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-77df-98be-f6e089b39779" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019d8775-5dfd-7b8e-a247-7a435357fbdb" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-77df-98be-f6e089b39779" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateSwapMember_019d8775-5dfd-7125-aeb9-ce2fa545c732" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestRateSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-77df-98be-f6e089b39779" xlink:to="loc_us-gaap_InterestRateSwapMember_019d8775-5dfd-7125-aeb9-ce2fa545c732" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignExchangeContractMember_019d8775-5dfd-7d8e-accc-c41b0decbc3d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ForeignExchangeContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019d8775-5dfd-77df-98be-f6e089b39779" xlink:to="loc_us-gaap_ForeignExchangeContractMember_019d8775-5dfd-7d8e-accc-c41b0decbc3d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnInvestments_019d8775-5dfd-7623-8878-90c01fe7fd41" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainLossOnInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems_019d8775-5dfd-743e-a8d5-2620f860f525" xlink:to="loc_us-gaap_GainLossOnInvestments_019d8775-5dfd-7623-8878-90c01fe7fd41" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_ImpairmentLossDebtSecuritiesAvailableForSale_019d8775-5dfd-7217-9c5d-34a52b746832" xlink:href="unm-20260331.xsd#unm_ImpairmentLossDebtSecuritiesAvailableForSale"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems_019d8775-5dfd-743e-a8d5-2620f860f525" xlink:to="loc_unm_ImpairmentLossDebtSecuritiesAvailableForSale_019d8775-5dfd-7217-9c5d-34a52b746832" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLossPeriodIncreaseDecrease_019d8775-5dfd-7234-808d-a5ef19a4cafc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLossPeriodIncreaseDecrease"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems_019d8775-5dfd-743e-a8d5-2620f860f525" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLossPeriodIncreaseDecrease_019d8775-5dfd-7234-808d-a5ef19a4cafc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetInvestmentIncome_019d8775-5dfd-7f4e-a14b-84c62935cce6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetInvestmentIncome"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems_019d8775-5dfd-743e-a8d5-2620f860f525" xlink:to="loc_us-gaap_NetInvestmentIncome_019d8775-5dfd-7f4e-a14b-84c62935cce6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherCostAndExpenseOperating_019d8775-5dfd-78e7-845a-267adbace6e9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherCostAndExpenseOperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems_019d8775-5dfd-743e-a8d5-2620f860f525" xlink:to="loc_us-gaap_OtherCostAndExpenseOperating_019d8775-5dfd-78e7-845a-267adbace6e9" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments_019d8775-5dfd-78aa-92e3-7ca9a8547dbf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems_019d8775-5dfd-743e-a8d5-2620f860f525" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments_019d8775-5dfd-78aa-92e3-7ca9a8547dbf" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_019d8775-5dfd-7727-87da-bc45b8c346e0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems_019d8775-5dfd-743e-a8d5-2620f860f525" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_019d8775-5dfd-7727-87da-bc45b8c346e0" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019d8775-5dfd-7b13-a167-b56c163289f9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems_019d8775-5dfd-743e-a8d5-2620f860f525" xlink:to="loc_us-gaap_NetIncomeLoss_019d8775-5dfd-7b13-a167-b56c163289f9" xlink:type="arc" order="7"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.unum.com/role/LiabilityforFuturePolicyBenefitActivityDetails" xlink:type="simple" xlink:href="unm-20260331.xsd#LiabilityforFuturePolicyBenefitActivityDetails"/>
  <link:definitionLink xlink:role="http://www.unum.com/role/LiabilityforFuturePolicyBenefitActivityDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForFuturePolicyBenefitActivityLineItems_019d8775-5dfd-7aed-ba15-ee3be94e87a7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilityForFuturePolicyBenefitActivityLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForFuturePolicyBenefitActivityTable_019d8775-5dfd-7d1f-b5b5-a7f943022b0d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilityForFuturePolicyBenefitActivityTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LiabilityForFuturePolicyBenefitActivityLineItems_019d8775-5dfd-7aed-ba15-ee3be94e87a7" xlink:to="loc_us-gaap_LiabilityForFuturePolicyBenefitActivityTable_019d8775-5dfd-7d1f-b5b5-a7f943022b0d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_019d8775-5dfd-70ea-bb3b-2b63c4758be4" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LiabilityForFuturePolicyBenefitActivityTable_019d8775-5dfd-7d1f-b5b5-a7f943022b0d" xlink:to="loc_srt_ConsolidationItemsAxis_019d8775-5dfd-70ea-bb3b-2b63c4758be4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019d8775-5dfd-70ea-bb3b-2b63c4758be4_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_019d8775-5dfd-70ea-bb3b-2b63c4758be4" xlink:to="loc_srt_ConsolidationItemsDomain_019d8775-5dfd-70ea-bb3b-2b63c4758be4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019d8775-5dfd-7ccf-b386-3fed767efa64" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_019d8775-5dfd-70ea-bb3b-2b63c4758be4" xlink:to="loc_srt_ConsolidationItemsDomain_019d8775-5dfd-7ccf-b386-3fed767efa64" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_019d8775-5dfd-7c9c-93d3-d0f90a0b4663" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_019d8775-5dfd-7ccf-b386-3fed767efa64" xlink:to="loc_us-gaap_OperatingSegmentsMember_019d8775-5dfd-7c9c-93d3-d0f90a0b4663" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_019d8775-5dfd-7f75-a87e-39185b834f7a" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LiabilityForFuturePolicyBenefitActivityTable_019d8775-5dfd-7d1f-b5b5-a7f943022b0d" xlink:to="loc_srt_ProductOrServiceAxis_019d8775-5dfd-7f75-a87e-39185b834f7a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019d8775-5dfd-7f75-a87e-39185b834f7a_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_019d8775-5dfd-7f75-a87e-39185b834f7a" xlink:to="loc_srt_ProductsAndServicesDomain_019d8775-5dfd-7f75-a87e-39185b834f7a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019d8775-5dfd-7abb-9a42-a3eb87cd23a6" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_019d8775-5dfd-7f75-a87e-39185b834f7a" xlink:to="loc_srt_ProductsAndServicesDomain_019d8775-5dfd-7abb-9a42-a3eb87cd23a6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_GroupDisabilityMember_019d8775-5dfd-7f1d-bf95-23d65ad0f4b3" xlink:href="unm-20260331.xsd#unm_GroupDisabilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019d8775-5dfd-7abb-9a42-a3eb87cd23a6" xlink:to="loc_unm_GroupDisabilityMember_019d8775-5dfd-7f1d-bf95-23d65ad0f4b3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_GroupLifeAndADDMember_019d8775-5dfd-70f5-ae97-a4b5dba46bcf" xlink:href="unm-20260331.xsd#unm_GroupLifeAndADDMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019d8775-5dfd-7abb-9a42-a3eb87cd23a6" xlink:to="loc_unm_GroupLifeAndADDMember_019d8775-5dfd-70f5-ae97-a4b5dba46bcf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_VoluntaryBenefitsMember_019d8775-5dfd-77d4-b0d2-79395c0e8a17" xlink:href="unm-20260331.xsd#unm_VoluntaryBenefitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019d8775-5dfd-7abb-9a42-a3eb87cd23a6" xlink:to="loc_unm_VoluntaryBenefitsMember_019d8775-5dfd-77d4-b0d2-79395c0e8a17" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_IndividualDisabilityMember_019d8775-5dfd-75e8-89cb-d6560242ba1b" xlink:href="unm-20260331.xsd#unm_IndividualDisabilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019d8775-5dfd-7abb-9a42-a3eb87cd23a6" xlink:to="loc_unm_IndividualDisabilityMember_019d8775-5dfd-75e8-89cb-d6560242ba1b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_LongTermCareMember_019d8775-5dfd-7806-af93-929edc58035c" xlink:href="unm-20260331.xsd#unm_LongTermCareMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019d8775-5dfd-7abb-9a42-a3eb87cd23a6" xlink:to="loc_unm_LongTermCareMember_019d8775-5dfd-7806-af93-929edc58035c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherInsuranceProductLineMember_019d8775-5dfd-77bd-8f02-e429733975e9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherInsuranceProductLineMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019d8775-5dfd-7abb-9a42-a3eb87cd23a6" xlink:to="loc_us-gaap_OtherInsuranceProductLineMember_019d8775-5dfd-77bd-8f02-e429733975e9" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019d8775-5dfd-7386-8d8c-bdd3e4296c81" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LiabilityForFuturePolicyBenefitActivityTable_019d8775-5dfd-7d1f-b5b5-a7f943022b0d" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019d8775-5dfd-7386-8d8c-bdd3e4296c81" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019d8775-5dfd-7386-8d8c-bdd3e4296c81_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019d8775-5dfd-7386-8d8c-bdd3e4296c81" xlink:to="loc_us-gaap_SegmentDomain_019d8775-5dfd-7386-8d8c-bdd3e4296c81_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019d8775-5dfd-7722-9449-88e2f8afc465" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019d8775-5dfd-7386-8d8c-bdd3e4296c81" xlink:to="loc_us-gaap_SegmentDomain_019d8775-5dfd-7722-9449-88e2f8afc465" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_UnumUsMember_019d8775-5dfd-7f0b-a48a-3bb2225a5d4f" xlink:href="unm-20260331.xsd#unm_UnumUsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019d8775-5dfd-7722-9449-88e2f8afc465" xlink:to="loc_unm_UnumUsMember_019d8775-5dfd-7f0b-a48a-3bb2225a5d4f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_UnumInternationalMember_019d8775-5dfd-7076-b4ef-c19534c0b59a" xlink:href="unm-20260331.xsd#unm_UnumInternationalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019d8775-5dfd-7722-9449-88e2f8afc465" xlink:to="loc_unm_UnumInternationalMember_019d8775-5dfd-7076-b4ef-c19534c0b59a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_ColonialLifeMember_019d8775-5dfd-73c7-a78f-6124a070d089" xlink:href="unm-20260331.xsd#unm_ColonialLifeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019d8775-5dfd-7722-9449-88e2f8afc465" xlink:to="loc_unm_ColonialLifeMember_019d8775-5dfd-73c7-a78f-6124a070d089" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_ClosedBlockMember_019d8775-5dfd-72a8-82e7-2ab62455e819" xlink:href="unm-20260331.xsd#unm_ClosedBlockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019d8775-5dfd-7722-9449-88e2f8afc465" xlink:to="loc_unm_ClosedBlockMember_019d8775-5dfd-72a8-82e7-2ab62455e819" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_OtherProductsMember_019d8775-5dfd-76b4-b6e0-35e6cf667703" xlink:href="unm-20260331.xsd#unm_OtherProductsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019d8775-5dfd-7722-9449-88e2f8afc465" xlink:to="loc_unm_OtherProductsMember_019d8775-5dfd-76b4-b6e0-35e6cf667703" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedNetPremiumRollForward_019d8775-5dfd-7d3b-905e-cbce5b762178" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilityForFuturePolicyBenefitExpectedNetPremiumRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForFuturePolicyBenefitActivityLineItems_019d8775-5dfd-7aed-ba15-ee3be94e87a7" xlink:to="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedNetPremiumRollForward_019d8775-5dfd-7d3b-905e-cbce5b762178" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedNetPremiumBeforeReinsuranceAfterDiscountRateChange_019d8775-5dfd-779e-b677-9e85b3f8883a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilityForFuturePolicyBenefitExpectedNetPremiumBeforeReinsuranceAfterDiscountRateChange"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedNetPremiumRollForward_019d8775-5dfd-7d3b-905e-cbce5b762178" xlink:to="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedNetPremiumBeforeReinsuranceAfterDiscountRateChange_019d8775-5dfd-779e-b677-9e85b3f8883a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedNetPremiumOriginalDiscountRateBeforeCashFlowAndReinsurance_019d8775-5dfd-7e4e-a51a-0135469ec40f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilityForFuturePolicyBenefitExpectedNetPremiumOriginalDiscountRateBeforeCashFlowAndReinsurance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedNetPremiumRollForward_019d8775-5dfd-7d3b-905e-cbce5b762178" xlink:to="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedNetPremiumOriginalDiscountRateBeforeCashFlowAndReinsurance_019d8775-5dfd-7e4e-a51a-0135469ec40f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedNetPremiumCumulativeIncreaseDecreaseFromCashFlowChange_019d8775-5dfd-794d-9ecb-9179a9c3d8f9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilityForFuturePolicyBenefitExpectedNetPremiumCumulativeIncreaseDecreaseFromCashFlowChange"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedNetPremiumRollForward_019d8775-5dfd-7d3b-905e-cbce5b762178" xlink:to="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedNetPremiumCumulativeIncreaseDecreaseFromCashFlowChange_019d8775-5dfd-794d-9ecb-9179a9c3d8f9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedNetPremiumCumulativeIncreaseDecreaseOfActualVarianceFromExpectedExperience_019d8775-5dfd-7fe5-a359-d512e2842b47" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilityForFuturePolicyBenefitExpectedNetPremiumCumulativeIncreaseDecreaseOfActualVarianceFromExpectedExperience"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedNetPremiumRollForward_019d8775-5dfd-7d3b-905e-cbce5b762178" xlink:to="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedNetPremiumCumulativeIncreaseDecreaseOfActualVarianceFromExpectedExperience_019d8775-5dfd-7fe5-a359-d512e2842b47" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedNetPremiumOriginalDiscountRateBeforeReinsuranceAfterCashFlowChange_019d8775-5dfd-7686-87e9-c4cda91bccad" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilityForFuturePolicyBenefitExpectedNetPremiumOriginalDiscountRateBeforeReinsuranceAfterCashFlowChange"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedNetPremiumRollForward_019d8775-5dfd-7d3b-905e-cbce5b762178" xlink:to="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedNetPremiumOriginalDiscountRateBeforeReinsuranceAfterCashFlowChange_019d8775-5dfd-7686-87e9-c4cda91bccad" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedNetPremiumIssuance_019d8775-5dfd-7e56-a452-711eacd7503c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilityForFuturePolicyBenefitExpectedNetPremiumIssuance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedNetPremiumRollForward_019d8775-5dfd-7d3b-905e-cbce5b762178" xlink:to="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedNetPremiumIssuance_019d8775-5dfd-7e56-a452-711eacd7503c" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedNetPremiumInterestIncome_019d8775-5dfd-7626-aa16-cd94d3e85ad1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilityForFuturePolicyBenefitExpectedNetPremiumInterestIncome"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedNetPremiumRollForward_019d8775-5dfd-7d3b-905e-cbce5b762178" xlink:to="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedNetPremiumInterestIncome_019d8775-5dfd-7626-aa16-cd94d3e85ad1" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedNetPremiumNetPremiumCollected_019d8775-5dfd-7a7b-bcbe-d05944804427" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilityForFuturePolicyBenefitExpectedNetPremiumNetPremiumCollected"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedNetPremiumRollForward_019d8775-5dfd-7d3b-905e-cbce5b762178" xlink:to="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedNetPremiumNetPremiumCollected_019d8775-5dfd-7a7b-bcbe-d05944804427" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedNetPremiumIncreaseDecreaseForOtherChange_019d8775-5dfd-7351-8335-f420a0748679" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilityForFuturePolicyBenefitExpectedNetPremiumIncreaseDecreaseForOtherChange"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedNetPremiumRollForward_019d8775-5dfd-7d3b-905e-cbce5b762178" xlink:to="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedNetPremiumIncreaseDecreaseForOtherChange_019d8775-5dfd-7351-8335-f420a0748679" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedNetPremiumOriginalDiscountRateBeforeCashFlowAndReinsurance_019d8775-5dfd-7673-83c0-b85025ce10cc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilityForFuturePolicyBenefitExpectedNetPremiumOriginalDiscountRateBeforeCashFlowAndReinsurance"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AociLiabilityForFuturePolicyBenefitExpectedNetPremiumBeforeTax_019d8775-5dfd-7e0d-bfed-8b7c88570a2a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AociLiabilityForFuturePolicyBenefitExpectedNetPremiumBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedNetPremiumRollForward_019d8775-5dfd-7d3b-905e-cbce5b762178" xlink:to="loc_us-gaap_AociLiabilityForFuturePolicyBenefitExpectedNetPremiumBeforeTax_019d8775-5dfd-7e0d-bfed-8b7c88570a2a" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedNetPremiumBeforeReinsuranceAfterDiscountRateChange_019d8775-5dfd-7913-af82-c814b13e1b53" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilityForFuturePolicyBenefitExpectedNetPremiumBeforeReinsuranceAfterDiscountRateChange"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedFuturePolicyBenefitRollForward_019d8775-5dfd-7d1d-bc2e-adf26dc4d3af" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilityForFuturePolicyBenefitExpectedFuturePolicyBenefitRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForFuturePolicyBenefitActivityLineItems_019d8775-5dfd-7aed-ba15-ee3be94e87a7" xlink:to="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedFuturePolicyBenefitRollForward_019d8775-5dfd-7d1d-bc2e-adf26dc4d3af" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedFuturePolicyBenefitBeforeReinsuranceAfterDiscountRateChange_019d8775-5dfd-780a-8757-ff7c4586a57f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilityForFuturePolicyBenefitExpectedFuturePolicyBenefitBeforeReinsuranceAfterDiscountRateChange"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedFuturePolicyBenefitRollForward_019d8775-5dfd-7d1d-bc2e-adf26dc4d3af" xlink:to="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedFuturePolicyBenefitBeforeReinsuranceAfterDiscountRateChange_019d8775-5dfd-780a-8757-ff7c4586a57f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedFuturePolicyBenefitOriginalDiscountRateBeforeCashFlowAndReinsurance_019d8775-5dfd-711e-a762-1c467aac16e0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilityForFuturePolicyBenefitExpectedFuturePolicyBenefitOriginalDiscountRateBeforeCashFlowAndReinsurance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedFuturePolicyBenefitRollForward_019d8775-5dfd-7d1d-bc2e-adf26dc4d3af" xlink:to="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedFuturePolicyBenefitOriginalDiscountRateBeforeCashFlowAndReinsurance_019d8775-5dfd-711e-a762-1c467aac16e0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedFuturePolicyBenefitCumulativeIncreaseDecreaseFromCashFlowChange_019d8775-5dfd-7022-b0e4-14d12ab786a1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilityForFuturePolicyBenefitExpectedFuturePolicyBenefitCumulativeIncreaseDecreaseFromCashFlowChange"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedFuturePolicyBenefitRollForward_019d8775-5dfd-7d1d-bc2e-adf26dc4d3af" xlink:to="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedFuturePolicyBenefitCumulativeIncreaseDecreaseFromCashFlowChange_019d8775-5dfd-7022-b0e4-14d12ab786a1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedFuturePolicyBenefitCumulativeIncreaseDecreaseOfActualVarianceFromExpectedExperience_019d8775-5dfd-7bff-b1e4-53aa024fea53" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilityForFuturePolicyBenefitExpectedFuturePolicyBenefitCumulativeIncreaseDecreaseOfActualVarianceFromExpectedExperience"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedFuturePolicyBenefitRollForward_019d8775-5dfd-7d1d-bc2e-adf26dc4d3af" xlink:to="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedFuturePolicyBenefitCumulativeIncreaseDecreaseOfActualVarianceFromExpectedExperience_019d8775-5dfd-7bff-b1e4-53aa024fea53" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedFutureBenefitOriginalDiscountRateBeforeReinsuranceAfterCashFlowChange_019d8775-5dfd-76bb-87b5-1314ae8153b2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilityForFuturePolicyBenefitExpectedFutureBenefitOriginalDiscountRateBeforeReinsuranceAfterCashFlowChange"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedFuturePolicyBenefitRollForward_019d8775-5dfd-7d1d-bc2e-adf26dc4d3af" xlink:to="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedFutureBenefitOriginalDiscountRateBeforeReinsuranceAfterCashFlowChange_019d8775-5dfd-76bb-87b5-1314ae8153b2" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedFuturePolicyBenefitIssuance_019d8775-5dfd-72fd-9e32-a6e64d7d0807" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilityForFuturePolicyBenefitExpectedFuturePolicyBenefitIssuance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedFuturePolicyBenefitRollForward_019d8775-5dfd-7d1d-bc2e-adf26dc4d3af" xlink:to="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedFuturePolicyBenefitIssuance_019d8775-5dfd-72fd-9e32-a6e64d7d0807" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedFuturePolicyBenefitInterestExpense_019d8775-5dfd-7638-a06c-93841f2cba69" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilityForFuturePolicyBenefitExpectedFuturePolicyBenefitInterestExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedFuturePolicyBenefitRollForward_019d8775-5dfd-7d1d-bc2e-adf26dc4d3af" xlink:to="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedFuturePolicyBenefitInterestExpense_019d8775-5dfd-7638-a06c-93841f2cba69" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForFuturePolicyBenefitsPaymentForBenefits_019d8775-5dfd-701f-b169-b1b48fbb1b1d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilityForFuturePolicyBenefitsPaymentForBenefits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedFuturePolicyBenefitRollForward_019d8775-5dfd-7d1d-bc2e-adf26dc4d3af" xlink:to="loc_us-gaap_LiabilityForFuturePolicyBenefitsPaymentForBenefits_019d8775-5dfd-701f-b169-b1b48fbb1b1d" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedFuturePolicyBenefitIncreaseDecreaseForOtherChange_019d8775-5dfd-70bf-9f34-0ea082aebb10" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilityForFuturePolicyBenefitExpectedFuturePolicyBenefitIncreaseDecreaseForOtherChange"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedFuturePolicyBenefitRollForward_019d8775-5dfd-7d1d-bc2e-adf26dc4d3af" xlink:to="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedFuturePolicyBenefitIncreaseDecreaseForOtherChange_019d8775-5dfd-70bf-9f34-0ea082aebb10" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedFuturePolicyBenefitOriginalDiscountRateBeforeCashFlowAndReinsurance_019d8775-5dfd-7772-9461-e3e53fa0be37" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilityForFuturePolicyBenefitExpectedFuturePolicyBenefitOriginalDiscountRateBeforeCashFlowAndReinsurance"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AociLiabilityForFuturePolicyBenefitExpectedFuturePolicyBenefitBeforeTax_019d8775-5dfd-7854-99a9-7109b95ab21c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AociLiabilityForFuturePolicyBenefitExpectedFuturePolicyBenefitBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedFuturePolicyBenefitRollForward_019d8775-5dfd-7d1d-bc2e-adf26dc4d3af" xlink:to="loc_us-gaap_AociLiabilityForFuturePolicyBenefitExpectedFuturePolicyBenefitBeforeTax_019d8775-5dfd-7854-99a9-7109b95ab21c" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedFuturePolicyBenefitBeforeReinsuranceAfterDiscountRateChange_019d8775-5dfd-75c6-b43b-5e40cd66427a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilityForFuturePolicyBenefitExpectedFuturePolicyBenefitBeforeReinsuranceAfterDiscountRateChange"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_LiabilityForFuturePolicyBenefitBeforeReinsuranceBeforeOther_019d8775-5dfd-7b4c-a2c3-44401276e73b" xlink:href="unm-20260331.xsd#unm_LiabilityForFuturePolicyBenefitBeforeReinsuranceBeforeOther"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedFuturePolicyBenefitRollForward_019d8775-5dfd-7d1d-bc2e-adf26dc4d3af" xlink:to="loc_unm_LiabilityForFuturePolicyBenefitBeforeReinsuranceBeforeOther_019d8775-5dfd-7b4c-a2c3-44401276e73b" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_LiabilityForFuturePolicyBenefitOther_019d8775-5dfd-7dc9-9e59-f918880217ef" xlink:href="unm-20260331.xsd#unm_LiabilityForFuturePolicyBenefitOther"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedFuturePolicyBenefitRollForward_019d8775-5dfd-7d1d-bc2e-adf26dc4d3af" xlink:to="loc_unm_LiabilityForFuturePolicyBenefitOther_019d8775-5dfd-7dc9-9e59-f918880217ef" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_LiabilityForFuturePolicyBenefitBeforeReinsuranceAfterOther_019d8775-5dfd-743e-8654-7ca30ad2dc99" xlink:href="unm-20260331.xsd#unm_LiabilityForFuturePolicyBenefitBeforeReinsuranceAfterOther"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedFuturePolicyBenefitRollForward_019d8775-5dfd-7d1d-bc2e-adf26dc4d3af" xlink:to="loc_unm_LiabilityForFuturePolicyBenefitBeforeReinsuranceAfterOther_019d8775-5dfd-743e-8654-7ca30ad2dc99" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForFuturePolicyBenefitReinsuranceRecoverableAfterAllowance_019d8775-5dfd-7c49-b0c7-2843074c7717" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilityForFuturePolicyBenefitReinsuranceRecoverableAfterAllowance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedFuturePolicyBenefitRollForward_019d8775-5dfd-7d1d-bc2e-adf26dc4d3af" xlink:to="loc_us-gaap_LiabilityForFuturePolicyBenefitReinsuranceRecoverableAfterAllowance_019d8775-5dfd-7c49-b0c7-2843074c7717" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForFuturePolicyBenefitAfterReinsurance_019d8775-5dfd-71a4-a9c2-f31c55fdfdb0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilityForFuturePolicyBenefitAfterReinsurance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedFuturePolicyBenefitRollForward_019d8775-5dfd-7d1d-bc2e-adf26dc4d3af" xlink:to="loc_us-gaap_LiabilityForFuturePolicyBenefitAfterReinsurance_019d8775-5dfd-71a4-a9c2-f31c55fdfdb0" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForFuturePolicyBenefitGrossPremiumIncome_019d8775-5dfd-7c2c-83de-f23ad5f6d607" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilityForFuturePolicyBenefitGrossPremiumIncome"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForFuturePolicyBenefitActivityLineItems_019d8775-5dfd-7aed-ba15-ee3be94e87a7" xlink:to="loc_us-gaap_LiabilityForFuturePolicyBenefitGrossPremiumIncome_019d8775-5dfd-7c2c-83de-f23ad5f6d607" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForFuturePolicyBenefitInterestExpense_019d8775-5dfd-78bd-b023-36b4d5b3f8aa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilityForFuturePolicyBenefitInterestExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForFuturePolicyBenefitActivityLineItems_019d8775-5dfd-7aed-ba15-ee3be94e87a7" xlink:to="loc_us-gaap_LiabilityForFuturePolicyBenefitInterestExpense_019d8775-5dfd-78bd-b023-36b4d5b3f8aa" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedFuturePolicyBenefitUndiscountedBeforeReinsurance_019d8775-5dfd-7287-8f71-782e0eb28b2e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilityForFuturePolicyBenefitExpectedFuturePolicyBenefitUndiscountedBeforeReinsurance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForFuturePolicyBenefitActivityLineItems_019d8775-5dfd-7aed-ba15-ee3be94e87a7" xlink:to="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedFuturePolicyBenefitUndiscountedBeforeReinsurance_019d8775-5dfd-7287-8f71-782e0eb28b2e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedFutureGrossPremiumUndiscountedBeforeReinsurance_019d8775-5dfd-76e2-8aa4-99839e3b16bd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilityForFuturePolicyBenefitExpectedFutureGrossPremiumUndiscountedBeforeReinsurance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForFuturePolicyBenefitActivityLineItems_019d8775-5dfd-7aed-ba15-ee3be94e87a7" xlink:to="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedFutureGrossPremiumUndiscountedBeforeReinsurance_019d8775-5dfd-76e2-8aa4-99839e3b16bd" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedFutureGrossPremiumDiscountedBeforeReinsurance_019d8775-5dfd-771a-991c-054522547bc2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilityForFuturePolicyBenefitExpectedFutureGrossPremiumDiscountedBeforeReinsurance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForFuturePolicyBenefitActivityLineItems_019d8775-5dfd-7aed-ba15-ee3be94e87a7" xlink:to="loc_us-gaap_LiabilityForFuturePolicyBenefitExpectedFutureGrossPremiumDiscountedBeforeReinsurance_019d8775-5dfd-771a-991c-054522547bc2" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForFuturePolicyBenefitWeightedAverageInterestAccretionRate_019d8775-5dfd-7574-83db-2b77933e68f0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilityForFuturePolicyBenefitWeightedAverageInterestAccretionRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForFuturePolicyBenefitActivityLineItems_019d8775-5dfd-7aed-ba15-ee3be94e87a7" xlink:to="loc_us-gaap_LiabilityForFuturePolicyBenefitWeightedAverageInterestAccretionRate_019d8775-5dfd-7574-83db-2b77933e68f0" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForFuturePolicyBenefitCurrentWeightedAverageDiscountRate_019d8775-5dfd-7a03-a023-cadf0000640e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilityForFuturePolicyBenefitCurrentWeightedAverageDiscountRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForFuturePolicyBenefitActivityLineItems_019d8775-5dfd-7aed-ba15-ee3be94e87a7" xlink:to="loc_us-gaap_LiabilityForFuturePolicyBenefitCurrentWeightedAverageDiscountRate_019d8775-5dfd-7a03-a023-cadf0000640e" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForFuturePolicyBenefitWeightedAverageDuration_019d8775-5dfd-7b78-bc76-d0bec35a83d0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilityForFuturePolicyBenefitWeightedAverageDuration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForFuturePolicyBenefitActivityLineItems_019d8775-5dfd-7aed-ba15-ee3be94e87a7" xlink:to="loc_us-gaap_LiabilityForFuturePolicyBenefitWeightedAverageDuration_019d8775-5dfd-7b78-bc76-d0bec35a83d0" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForFuturePolicyBenefits_019d8775-5dfd-7514-9b14-97843cd068b4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilityForFuturePolicyBenefits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForFuturePolicyBenefitActivityLineItems_019d8775-5dfd-7aed-ba15-ee3be94e87a7" xlink:to="loc_us-gaap_LiabilityForFuturePolicyBenefits_019d8775-5dfd-7514-9b14-97843cd068b4" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForFuturePolicyBenefitAdverseDevelopmentExpense_019dceaa-4fbc-7e75-a0d8-a4cfa0348855" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilityForFuturePolicyBenefitAdverseDevelopmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForFuturePolicyBenefitActivityLineItems_019d8775-5dfd-7aed-ba15-ee3be94e87a7" xlink:to="loc_us-gaap_LiabilityForFuturePolicyBenefitAdverseDevelopmentExpense_019dceaa-4fbc-7e75-a0d8-a4cfa0348855" xlink:type="arc" order="11"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.unum.com/role/PolicyholderAccountBalanceDetails" xlink:type="simple" xlink:href="unm-20260331.xsd#PolicyholderAccountBalanceDetails"/>
  <link:definitionLink xlink:role="http://www.unum.com/role/PolicyholderAccountBalanceDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PolicyholderAccountBalanceLineItems_019d8775-5dfd-7feb-a31a-a5614c7746b7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PolicyholderAccountBalanceLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PolicyholderAccountBalanceTable_019d8775-5dfd-7379-a653-c6a1553a3b1f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PolicyholderAccountBalanceTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PolicyholderAccountBalanceLineItems_019d8775-5dfd-7feb-a31a-a5614c7746b7" xlink:to="loc_us-gaap_PolicyholderAccountBalanceTable_019d8775-5dfd-7379-a653-c6a1553a3b1f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_019d8775-5dfd-7909-b17a-e1fadff95790" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_PolicyholderAccountBalanceTable_019d8775-5dfd-7379-a653-c6a1553a3b1f" xlink:to="loc_srt_ProductOrServiceAxis_019d8775-5dfd-7909-b17a-e1fadff95790" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019d8775-5dfd-7909-b17a-e1fadff95790_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_019d8775-5dfd-7909-b17a-e1fadff95790" xlink:to="loc_srt_ProductsAndServicesDomain_019d8775-5dfd-7909-b17a-e1fadff95790_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019d8775-5dfd-7137-b6ef-2bd054d78776" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_019d8775-5dfd-7909-b17a-e1fadff95790" xlink:to="loc_srt_ProductsAndServicesDomain_019d8775-5dfd-7137-b6ef-2bd054d78776" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_VoluntaryBenefitsMember_019d8775-5dfd-712f-afa5-2f6905534198" xlink:href="unm-20260331.xsd#unm_VoluntaryBenefitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019d8775-5dfd-7137-b6ef-2bd054d78776" xlink:to="loc_unm_VoluntaryBenefitsMember_019d8775-5dfd-712f-afa5-2f6905534198" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherInsuranceProductLineMember_019d8775-5dfd-716a-ad3b-798d8ba44a3f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherInsuranceProductLineMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019d8775-5dfd-7137-b6ef-2bd054d78776" xlink:to="loc_us-gaap_OtherInsuranceProductLineMember_019d8775-5dfd-716a-ad3b-798d8ba44a3f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019d8775-5dfd-7f7f-b529-ef63a1e88482" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_PolicyholderAccountBalanceTable_019d8775-5dfd-7379-a653-c6a1553a3b1f" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019d8775-5dfd-7f7f-b529-ef63a1e88482" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019d8775-5dfd-7f7f-b529-ef63a1e88482_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019d8775-5dfd-7f7f-b529-ef63a1e88482" xlink:to="loc_us-gaap_SegmentDomain_019d8775-5dfd-7f7f-b529-ef63a1e88482_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019d8775-5dfd-77ea-bc96-1d2962849657" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019d8775-5dfd-7f7f-b529-ef63a1e88482" xlink:to="loc_us-gaap_SegmentDomain_019d8775-5dfd-77ea-bc96-1d2962849657" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_UnumUsMember_019d8775-5dfd-7a66-8c77-d5f0f38a3e8c" xlink:href="unm-20260331.xsd#unm_UnumUsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019d8775-5dfd-77ea-bc96-1d2962849657" xlink:to="loc_unm_UnumUsMember_019d8775-5dfd-7a66-8c77-d5f0f38a3e8c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_ColonialLifeMember_019d8775-5dfd-7fdd-9388-4109b081060b" xlink:href="unm-20260331.xsd#unm_ColonialLifeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019d8775-5dfd-77ea-bc96-1d2962849657" xlink:to="loc_unm_ColonialLifeMember_019d8775-5dfd-7fdd-9388-4109b081060b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_ClosedBlockMember_019d8775-5dfd-77dc-ae20-3274480dfa3b" xlink:href="unm-20260331.xsd#unm_ClosedBlockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019d8775-5dfd-77ea-bc96-1d2962849657" xlink:to="loc_unm_ClosedBlockMember_019d8775-5dfd-77dc-ae20-3274480dfa3b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_FundingAgreementsMember_019dceb2-9696-7ad7-af07-03e6d943b62d" xlink:href="unm-20260331.xsd#unm_FundingAgreementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019d8775-5dfd-77ea-bc96-1d2962849657" xlink:to="loc_unm_FundingAgreementsMember_019dceb2-9696-7ad7-af07-03e6d943b62d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_019d8775-5dfd-7b3e-9d03-7a4dd975a046" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_PolicyholderAccountBalanceTable_019d8775-5dfd-7379-a653-c6a1553a3b1f" xlink:to="loc_srt_ConsolidationItemsAxis_019d8775-5dfd-7b3e-9d03-7a4dd975a046" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019d8775-5dfd-7b3e-9d03-7a4dd975a046_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_019d8775-5dfd-7b3e-9d03-7a4dd975a046" xlink:to="loc_srt_ConsolidationItemsDomain_019d8775-5dfd-7b3e-9d03-7a4dd975a046_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019d8775-5dfd-7872-8a35-cea67114f0e9" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_019d8775-5dfd-7b3e-9d03-7a4dd975a046" xlink:to="loc_srt_ConsolidationItemsDomain_019d8775-5dfd-7872-8a35-cea67114f0e9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_019d8775-5dfd-7a15-b82f-66c936abfd39" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_019d8775-5dfd-7872-8a35-cea67114f0e9" xlink:to="loc_us-gaap_OperatingSegmentsMember_019d8775-5dfd-7a15-b82f-66c936abfd39" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PolicyholderAccountBalanceRollForward_019d8775-5dfd-7137-9d5c-f361b1d79918" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PolicyholderAccountBalanceRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PolicyholderAccountBalanceLineItems_019d8775-5dfd-7feb-a31a-a5614c7746b7" xlink:to="loc_us-gaap_PolicyholderAccountBalanceRollForward_019d8775-5dfd-7137-9d5c-f361b1d79918" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_PolicyholderAccountBalanceBeforeReservesInExcessOfAccountBalance_019d8775-5dfd-7229-b6c4-4e368339decc" xlink:href="unm-20260331.xsd#unm_PolicyholderAccountBalanceBeforeReservesInExcessOfAccountBalance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PolicyholderAccountBalanceRollForward_019d8775-5dfd-7137-9d5c-f361b1d79918" xlink:to="loc_unm_PolicyholderAccountBalanceBeforeReservesInExcessOfAccountBalance_019d8775-5dfd-7229-b6c4-4e368339decc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PolicyholderAccountBalancePremiumReceived_019d8775-5dfd-79b9-b03c-89a9d4aa464f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PolicyholderAccountBalancePremiumReceived"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PolicyholderAccountBalanceRollForward_019d8775-5dfd-7137-9d5c-f361b1d79918" xlink:to="loc_us-gaap_PolicyholderAccountBalancePremiumReceived_019d8775-5dfd-79b9-b03c-89a9d4aa464f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PolicyholderAccountBalancePolicyCharge_019d8775-5dfd-78c0-8a38-cc5f488d6478" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PolicyholderAccountBalancePolicyCharge"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PolicyholderAccountBalanceRollForward_019d8775-5dfd-7137-9d5c-f361b1d79918" xlink:to="loc_us-gaap_PolicyholderAccountBalancePolicyCharge_019d8775-5dfd-78c0-8a38-cc5f488d6478" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PolicyholderAccountBalanceSurrenderAndWithdrawal_019d8775-5dfd-7469-8e50-8d0e551504ec" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PolicyholderAccountBalanceSurrenderAndWithdrawal"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PolicyholderAccountBalanceRollForward_019d8775-5dfd-7137-9d5c-f361b1d79918" xlink:to="loc_us-gaap_PolicyholderAccountBalanceSurrenderAndWithdrawal_019d8775-5dfd-7469-8e50-8d0e551504ec" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PolicyholderAccountBalanceBenefitPayment_019d8775-5dfd-78fa-b468-ab62535d12ba" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PolicyholderAccountBalanceBenefitPayment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PolicyholderAccountBalanceRollForward_019d8775-5dfd-7137-9d5c-f361b1d79918" xlink:to="loc_us-gaap_PolicyholderAccountBalanceBenefitPayment_019d8775-5dfd-78fa-b468-ab62535d12ba" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestCreditedToPolicyholdersAccountBalances_019d8775-5dfd-7295-9d74-b20ce83198c5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestCreditedToPolicyholdersAccountBalances"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PolicyholderAccountBalanceRollForward_019d8775-5dfd-7137-9d5c-f361b1d79918" xlink:to="loc_us-gaap_InterestCreditedToPolicyholdersAccountBalances_019d8775-5dfd-7295-9d74-b20ce83198c5" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PolicyholderAccountBalanceIncreaseDecreaseFromOtherChange_019d8775-5dfd-73a6-9632-98dd718f7068" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PolicyholderAccountBalanceIncreaseDecreaseFromOtherChange"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PolicyholderAccountBalanceRollForward_019d8775-5dfd-7137-9d5c-f361b1d79918" xlink:to="loc_us-gaap_PolicyholderAccountBalanceIncreaseDecreaseFromOtherChange_019d8775-5dfd-73a6-9632-98dd718f7068" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_PolicyholderAccountBalanceBeforeReservesInExcessOfAccountBalance_019d8775-5dfd-7ad6-acfb-8999e8239199" xlink:href="unm-20260331.xsd#unm_PolicyholderAccountBalanceBeforeReservesInExcessOfAccountBalance"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_PolicyholderAccountBalanceReservesInExcessOfAccountBalance_019d8775-5dfd-717b-a191-2a70d03c30fe" xlink:href="unm-20260331.xsd#unm_PolicyholderAccountBalanceReservesInExcessOfAccountBalance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PolicyholderAccountBalanceRollForward_019d8775-5dfd-7137-9d5c-f361b1d79918" xlink:to="loc_unm_PolicyholderAccountBalanceReservesInExcessOfAccountBalance_019d8775-5dfd-717b-a191-2a70d03c30fe" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_TotalPolicyholdersAccountBalancesAfterReservesInExcessOfAccountBalance_019dcebd-f424-7ece-b0b2-03f182a9960f" xlink:href="unm-20260331.xsd#unm_TotalPolicyholdersAccountBalancesAfterReservesInExcessOfAccountBalance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PolicyholderAccountBalanceRollForward_019d8775-5dfd-7137-9d5c-f361b1d79918" xlink:to="loc_unm_TotalPolicyholdersAccountBalancesAfterReservesInExcessOfAccountBalance_019dcebd-f424-7ece-b0b2-03f182a9960f" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_PolicyholderAccountBalanceReinsuranceRecoverable_019d8775-5dfd-77dc-bd55-9b0efc69b26a" xlink:href="unm-20260331.xsd#unm_PolicyholderAccountBalanceReinsuranceRecoverable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PolicyholderAccountBalanceRollForward_019d8775-5dfd-7137-9d5c-f361b1d79918" xlink:to="loc_unm_PolicyholderAccountBalanceReinsuranceRecoverable_019d8775-5dfd-77dc-bd55-9b0efc69b26a" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_PolicyholderAccountBalanceAfterReinsuranceRecoverable_019d8775-5dfd-72d7-896f-d0069aacb67c" xlink:href="unm-20260331.xsd#unm_PolicyholderAccountBalanceAfterReinsuranceRecoverable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PolicyholderAccountBalanceRollForward_019d8775-5dfd-7137-9d5c-f361b1d79918" xlink:to="loc_unm_PolicyholderAccountBalanceAfterReinsuranceRecoverable_019d8775-5dfd-72d7-896f-d0069aacb67c" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PolicyholderAccountBalanceWeightedAverageCreditingRate_019d8775-5dfd-7e55-a088-a59e65518f25" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PolicyholderAccountBalanceWeightedAverageCreditingRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PolicyholderAccountBalanceLineItems_019d8775-5dfd-7feb-a31a-a5614c7746b7" xlink:to="loc_us-gaap_PolicyholderAccountBalanceWeightedAverageCreditingRate_019d8775-5dfd-7e55-a088-a59e65518f25" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PolicyholderAccountBalanceNetAmountAtRisk_019d8775-5dfd-7923-8c45-c57ff5c262d0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PolicyholderAccountBalanceNetAmountAtRisk"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PolicyholderAccountBalanceLineItems_019d8775-5dfd-7feb-a31a-a5614c7746b7" xlink:to="loc_us-gaap_PolicyholderAccountBalanceNetAmountAtRisk_019d8775-5dfd-7923-8c45-c57ff5c262d0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashSurrenderValueDuePolicyholdersAmount_019d8775-5dfd-734a-8107-bb9bfea7bd93" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashSurrenderValueDuePolicyholdersAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PolicyholderAccountBalanceLineItems_019d8775-5dfd-7feb-a31a-a5614c7746b7" xlink:to="loc_us-gaap_CashSurrenderValueDuePolicyholdersAmount_019d8775-5dfd-734a-8107-bb9bfea7bd93" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PolicyholderFunds_019d8775-5dfd-7cc8-801e-6001c547e0da" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PolicyholderFunds"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PolicyholderAccountBalanceLineItems_019d8775-5dfd-7feb-a31a-a5614c7746b7" xlink:to="loc_us-gaap_PolicyholderFunds_019d8775-5dfd-7cc8-801e-6001c547e0da" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.unum.com/role/PolicyholderAccountBalanceGuaranteedMinimumCreditingDetails" xlink:type="simple" xlink:href="unm-20260331.xsd#PolicyholderAccountBalanceGuaranteedMinimumCreditingDetails"/>
  <link:definitionLink xlink:role="http://www.unum.com/role/PolicyholderAccountBalanceGuaranteedMinimumCreditingDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PolicyholderAccountBalanceGuaranteedMinimumCreditingRateLineItems_019d8775-5dfd-7458-b466-86914e9b873f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PolicyholderAccountBalanceGuaranteedMinimumCreditingRateLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PolicyholderAccountBalanceGuaranteedMinimumCreditingRateTable_019d8775-5dfd-79cd-aaf0-e4756f7a5845" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PolicyholderAccountBalanceGuaranteedMinimumCreditingRateTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PolicyholderAccountBalanceGuaranteedMinimumCreditingRateLineItems_019d8775-5dfd-7458-b466-86914e9b873f" xlink:to="loc_us-gaap_PolicyholderAccountBalanceGuaranteedMinimumCreditingRateTable_019d8775-5dfd-79cd-aaf0-e4756f7a5845" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PolicyholderAccountBalanceAboveGuaranteedMinimumCreditingRateAxis_019d8775-5dfd-7b21-8907-d47b5f0de929" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PolicyholderAccountBalanceAboveGuaranteedMinimumCreditingRateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_PolicyholderAccountBalanceGuaranteedMinimumCreditingRateTable_019d8775-5dfd-79cd-aaf0-e4756f7a5845" xlink:to="loc_us-gaap_PolicyholderAccountBalanceAboveGuaranteedMinimumCreditingRateAxis_019d8775-5dfd-7b21-8907-d47b5f0de929" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PolicyholderAccountBalanceAboveGuaranteedMinimumCreditingRateDomain_019d8775-5dfd-7b21-8907-d47b5f0de929_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PolicyholderAccountBalanceAboveGuaranteedMinimumCreditingRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PolicyholderAccountBalanceAboveGuaranteedMinimumCreditingRateAxis_019d8775-5dfd-7b21-8907-d47b5f0de929" xlink:to="loc_us-gaap_PolicyholderAccountBalanceAboveGuaranteedMinimumCreditingRateDomain_019d8775-5dfd-7b21-8907-d47b5f0de929_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PolicyholderAccountBalanceAboveGuaranteedMinimumCreditingRateDomain_019d8775-5dfd-722f-84a7-022ba55dc6be" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PolicyholderAccountBalanceAboveGuaranteedMinimumCreditingRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PolicyholderAccountBalanceAboveGuaranteedMinimumCreditingRateAxis_019d8775-5dfd-7b21-8907-d47b5f0de929" xlink:to="loc_us-gaap_PolicyholderAccountBalanceAboveGuaranteedMinimumCreditingRateDomain_019d8775-5dfd-722f-84a7-022ba55dc6be" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PolicyholderAccountBalanceAtGuaranteedMinimumCreditingRateMember_019d8775-5dfd-7f83-85e9-f6c069816af6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PolicyholderAccountBalanceAtGuaranteedMinimumCreditingRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PolicyholderAccountBalanceAboveGuaranteedMinimumCreditingRateDomain_019d8775-5dfd-722f-84a7-022ba55dc6be" xlink:to="loc_us-gaap_PolicyholderAccountBalanceAtGuaranteedMinimumCreditingRateMember_019d8775-5dfd-7f83-85e9-f6c069816af6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PolicyholderAccountBalanceAboveGuaranteedMinimumCreditingRateRangeFrom0001To0050Member_019d8775-5dfd-75d5-bd97-f9d97b4a29ab" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PolicyholderAccountBalanceAboveGuaranteedMinimumCreditingRateRangeFrom0001To0050Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PolicyholderAccountBalanceAboveGuaranteedMinimumCreditingRateDomain_019d8775-5dfd-722f-84a7-022ba55dc6be" xlink:to="loc_us-gaap_PolicyholderAccountBalanceAboveGuaranteedMinimumCreditingRateRangeFrom0001To0050Member_019d8775-5dfd-75d5-bd97-f9d97b4a29ab" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PolicyholderAccountBalanceAboveGuaranteedMinimumCreditingRateRangeFrom0051To0150Member_019d8775-5dfd-776c-b080-6e4974a6e753" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PolicyholderAccountBalanceAboveGuaranteedMinimumCreditingRateRangeFrom0051To0150Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PolicyholderAccountBalanceAboveGuaranteedMinimumCreditingRateDomain_019d8775-5dfd-722f-84a7-022ba55dc6be" xlink:to="loc_us-gaap_PolicyholderAccountBalanceAboveGuaranteedMinimumCreditingRateRangeFrom0051To0150Member_019d8775-5dfd-776c-b080-6e4974a6e753" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PolicyholderAccountBalanceAboveGuaranteedMinimumCreditingRateRangeFrom0151AndGreaterMember_019d8775-5dfd-7fb9-860e-b6eb705a4526" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PolicyholderAccountBalanceAboveGuaranteedMinimumCreditingRateRangeFrom0151AndGreaterMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PolicyholderAccountBalanceAboveGuaranteedMinimumCreditingRateDomain_019d8775-5dfd-722f-84a7-022ba55dc6be" xlink:to="loc_us-gaap_PolicyholderAccountBalanceAboveGuaranteedMinimumCreditingRateRangeFrom0151AndGreaterMember_019d8775-5dfd-7fb9-860e-b6eb705a4526" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PolicyholderAccountBalanceGuaranteedMinimumCreditingRateRangeAxis_019d8775-5dfd-7ad3-ab54-c0dbf7180281" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PolicyholderAccountBalanceGuaranteedMinimumCreditingRateRangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_PolicyholderAccountBalanceGuaranteedMinimumCreditingRateTable_019d8775-5dfd-79cd-aaf0-e4756f7a5845" xlink:to="loc_us-gaap_PolicyholderAccountBalanceGuaranteedMinimumCreditingRateRangeAxis_019d8775-5dfd-7ad3-ab54-c0dbf7180281" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PolicyholderAccountBalanceGuaranteedMinimumCreditingRateRangeDomain_019d8775-5dfd-7ad3-ab54-c0dbf7180281_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PolicyholderAccountBalanceGuaranteedMinimumCreditingRateRangeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PolicyholderAccountBalanceGuaranteedMinimumCreditingRateRangeAxis_019d8775-5dfd-7ad3-ab54-c0dbf7180281" xlink:to="loc_us-gaap_PolicyholderAccountBalanceGuaranteedMinimumCreditingRateRangeDomain_019d8775-5dfd-7ad3-ab54-c0dbf7180281_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PolicyholderAccountBalanceGuaranteedMinimumCreditingRateRangeDomain_019d8775-5dfd-77f5-90ea-3fabb3eed0e9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PolicyholderAccountBalanceGuaranteedMinimumCreditingRateRangeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PolicyholderAccountBalanceGuaranteedMinimumCreditingRateRangeAxis_019d8775-5dfd-7ad3-ab54-c0dbf7180281" xlink:to="loc_us-gaap_PolicyholderAccountBalanceGuaranteedMinimumCreditingRateRangeDomain_019d8775-5dfd-77f5-90ea-3fabb3eed0e9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PolicyholderAccountBalanceGuaranteedMinimumCreditingRateRangeFrom0300To0399Member_019d8775-5dfd-7f59-9091-966032cd799a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PolicyholderAccountBalanceGuaranteedMinimumCreditingRateRangeFrom0300To0399Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PolicyholderAccountBalanceGuaranteedMinimumCreditingRateRangeDomain_019d8775-5dfd-77f5-90ea-3fabb3eed0e9" xlink:to="loc_us-gaap_PolicyholderAccountBalanceGuaranteedMinimumCreditingRateRangeFrom0300To0399Member_019d8775-5dfd-7f59-9091-966032cd799a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_PolicyholderAccountBalanceGuaranteedMinimumCreditingRateRangeFrom0400And0499Member_019d8775-5dfd-72d2-ab5d-d39a72ef9291" xlink:href="unm-20260331.xsd#unm_PolicyholderAccountBalanceGuaranteedMinimumCreditingRateRangeFrom0400And0499Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PolicyholderAccountBalanceGuaranteedMinimumCreditingRateRangeDomain_019d8775-5dfd-77f5-90ea-3fabb3eed0e9" xlink:to="loc_unm_PolicyholderAccountBalanceGuaranteedMinimumCreditingRateRangeFrom0400And0499Member_019d8775-5dfd-72d2-ab5d-d39a72ef9291" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_PolicyholderAccountBalanceGuaranteedMinimumCreditingRateRangeFrom0500And0600Member_019d8775-5dfd-7cfd-a0c4-6448a65fac0a" xlink:href="unm-20260331.xsd#unm_PolicyholderAccountBalanceGuaranteedMinimumCreditingRateRangeFrom0500And0600Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PolicyholderAccountBalanceGuaranteedMinimumCreditingRateRangeDomain_019d8775-5dfd-77f5-90ea-3fabb3eed0e9" xlink:to="loc_unm_PolicyholderAccountBalanceGuaranteedMinimumCreditingRateRangeFrom0500And0600Member_019d8775-5dfd-7cfd-a0c4-6448a65fac0a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_PolicyholderAccountBalanceGuaranteedMinimumCreditingRateRangeFrom0400And0500Member_019d8775-5dfd-7110-ae72-d4c592fc646e" xlink:href="unm-20260331.xsd#unm_PolicyholderAccountBalanceGuaranteedMinimumCreditingRateRangeFrom0400And0500Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PolicyholderAccountBalanceGuaranteedMinimumCreditingRateRangeDomain_019d8775-5dfd-77f5-90ea-3fabb3eed0e9" xlink:to="loc_unm_PolicyholderAccountBalanceGuaranteedMinimumCreditingRateRangeFrom0400And0500Member_019d8775-5dfd-7110-ae72-d4c592fc646e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_PolicyholderAccountBalanceGuaranteedMinimumCreditingRateRangeFrom0300And0599Member_019d8775-5dfd-76a4-8988-3111eb5dfbb8" xlink:href="unm-20260331.xsd#unm_PolicyholderAccountBalanceGuaranteedMinimumCreditingRateRangeFrom0300And0599Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PolicyholderAccountBalanceGuaranteedMinimumCreditingRateRangeDomain_019d8775-5dfd-77f5-90ea-3fabb3eed0e9" xlink:to="loc_unm_PolicyholderAccountBalanceGuaranteedMinimumCreditingRateRangeFrom0300And0599Member_019d8775-5dfd-76a4-8988-3111eb5dfbb8" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_PolicyholderAccountBalanceGuaranteedMinimumCreditingRateRangeFrom0600And0899Member_019d8775-5dfd-757f-bb5f-6a094a2272ff" xlink:href="unm-20260331.xsd#unm_PolicyholderAccountBalanceGuaranteedMinimumCreditingRateRangeFrom0600And0899Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PolicyholderAccountBalanceGuaranteedMinimumCreditingRateRangeDomain_019d8775-5dfd-77f5-90ea-3fabb3eed0e9" xlink:to="loc_unm_PolicyholderAccountBalanceGuaranteedMinimumCreditingRateRangeFrom0600And0899Member_019d8775-5dfd-757f-bb5f-6a094a2272ff" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_PolicyholderAccountBalanceGuaranteedMinimumCreditingRateRangeFrom0900And1199Member_019d8775-5dfd-7627-baff-33f6857b25ef" xlink:href="unm-20260331.xsd#unm_PolicyholderAccountBalanceGuaranteedMinimumCreditingRateRangeFrom0900And1199Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PolicyholderAccountBalanceGuaranteedMinimumCreditingRateRangeDomain_019d8775-5dfd-77f5-90ea-3fabb3eed0e9" xlink:to="loc_unm_PolicyholderAccountBalanceGuaranteedMinimumCreditingRateRangeFrom0900And1199Member_019d8775-5dfd-7627-baff-33f6857b25ef" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_PolicyholderAccountBalanceGuaranteedMinimumCreditingRateRangeFrom1200And1500Member_019d8775-5dfd-7e4c-95d2-3c7de04b1e6d" xlink:href="unm-20260331.xsd#unm_PolicyholderAccountBalanceGuaranteedMinimumCreditingRateRangeFrom1200And1500Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PolicyholderAccountBalanceGuaranteedMinimumCreditingRateRangeDomain_019d8775-5dfd-77f5-90ea-3fabb3eed0e9" xlink:to="loc_unm_PolicyholderAccountBalanceGuaranteedMinimumCreditingRateRangeFrom1200And1500Member_019d8775-5dfd-7e4c-95d2-3c7de04b1e6d" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019d8775-5dfd-7933-aa05-a58fd34c77cb" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_PolicyholderAccountBalanceGuaranteedMinimumCreditingRateTable_019d8775-5dfd-79cd-aaf0-e4756f7a5845" xlink:to="loc_srt_RangeAxis_019d8775-5dfd-7933-aa05-a58fd34c77cb" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019d8775-5dfd-7933-aa05-a58fd34c77cb_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019d8775-5dfd-7933-aa05-a58fd34c77cb" xlink:to="loc_srt_RangeMember_019d8775-5dfd-7933-aa05-a58fd34c77cb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019d8775-5dfd-73bb-a405-ab4e96562d8a" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019d8775-5dfd-7933-aa05-a58fd34c77cb" xlink:to="loc_srt_RangeMember_019d8775-5dfd-73bb-a405-ab4e96562d8a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019d8775-5dfd-73ad-9a12-f2973072341a" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019d8775-5dfd-73bb-a405-ab4e96562d8a" xlink:to="loc_srt_MinimumMember_019d8775-5dfd-73ad-9a12-f2973072341a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019d8775-5dfd-7e22-97ad-8888a168528a" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019d8775-5dfd-73bb-a405-ab4e96562d8a" xlink:to="loc_srt_MaximumMember_019d8775-5dfd-7e22-97ad-8888a168528a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_019d8775-5dfd-736b-8664-3ba24664d900" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_PolicyholderAccountBalanceGuaranteedMinimumCreditingRateTable_019d8775-5dfd-79cd-aaf0-e4756f7a5845" xlink:to="loc_srt_ProductOrServiceAxis_019d8775-5dfd-736b-8664-3ba24664d900" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019d8775-5dfd-736b-8664-3ba24664d900_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_019d8775-5dfd-736b-8664-3ba24664d900" xlink:to="loc_srt_ProductsAndServicesDomain_019d8775-5dfd-736b-8664-3ba24664d900_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019d8775-5dfd-728b-8506-330bc4e9a15b" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_019d8775-5dfd-736b-8664-3ba24664d900" xlink:to="loc_srt_ProductsAndServicesDomain_019d8775-5dfd-728b-8506-330bc4e9a15b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_VoluntaryBenefitsMember_019d8775-5dfd-719e-84cf-dcb0360e07ea" xlink:href="unm-20260331.xsd#unm_VoluntaryBenefitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019d8775-5dfd-728b-8506-330bc4e9a15b" xlink:to="loc_unm_VoluntaryBenefitsMember_019d8775-5dfd-719e-84cf-dcb0360e07ea" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherInsuranceProductLineMember_019d8775-5dfd-724d-aa33-099fc020f48a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherInsuranceProductLineMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019d8775-5dfd-728b-8506-330bc4e9a15b" xlink:to="loc_us-gaap_OtherInsuranceProductLineMember_019d8775-5dfd-724d-aa33-099fc020f48a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019d8775-5dfd-7024-995c-15ae3ae85be6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_PolicyholderAccountBalanceGuaranteedMinimumCreditingRateTable_019d8775-5dfd-79cd-aaf0-e4756f7a5845" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019d8775-5dfd-7024-995c-15ae3ae85be6" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019d8775-5dfd-7024-995c-15ae3ae85be6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019d8775-5dfd-7024-995c-15ae3ae85be6" xlink:to="loc_us-gaap_SegmentDomain_019d8775-5dfd-7024-995c-15ae3ae85be6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019d8775-5dfd-76b4-8274-f98a4d1fd6a3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019d8775-5dfd-7024-995c-15ae3ae85be6" xlink:to="loc_us-gaap_SegmentDomain_019d8775-5dfd-76b4-8274-f98a4d1fd6a3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_UnumUsMember_019d8775-5dfd-73fb-94dd-67396e2407e4" xlink:href="unm-20260331.xsd#unm_UnumUsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019d8775-5dfd-76b4-8274-f98a4d1fd6a3" xlink:to="loc_unm_UnumUsMember_019d8775-5dfd-73fb-94dd-67396e2407e4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_ColonialLifeMember_019d8775-5dfd-7998-ab01-7bc184df7c06" xlink:href="unm-20260331.xsd#unm_ColonialLifeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019d8775-5dfd-76b4-8274-f98a4d1fd6a3" xlink:to="loc_unm_ColonialLifeMember_019d8775-5dfd-7998-ab01-7bc184df7c06" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_ClosedBlockMember_019d8775-5dfd-7445-9d47-9eee27a1b9c4" xlink:href="unm-20260331.xsd#unm_ClosedBlockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019d8775-5dfd-76b4-8274-f98a4d1fd6a3" xlink:to="loc_unm_ClosedBlockMember_019d8775-5dfd-7445-9d47-9eee27a1b9c4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_019d8775-5dfd-71e5-9e15-b11847e2b9f8" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_PolicyholderAccountBalanceGuaranteedMinimumCreditingRateTable_019d8775-5dfd-79cd-aaf0-e4756f7a5845" xlink:to="loc_srt_ConsolidationItemsAxis_019d8775-5dfd-71e5-9e15-b11847e2b9f8" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019d8775-5dfd-71e5-9e15-b11847e2b9f8_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_019d8775-5dfd-71e5-9e15-b11847e2b9f8" xlink:to="loc_srt_ConsolidationItemsDomain_019d8775-5dfd-71e5-9e15-b11847e2b9f8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019d8775-5dfd-7d22-85d9-b1dc3f653b35" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_019d8775-5dfd-71e5-9e15-b11847e2b9f8" xlink:to="loc_srt_ConsolidationItemsDomain_019d8775-5dfd-7d22-85d9-b1dc3f653b35" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_019d8775-5dfd-7840-b05a-7855909d666b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_019d8775-5dfd-7d22-85d9-b1dc3f653b35" xlink:to="loc_us-gaap_OperatingSegmentsMember_019d8775-5dfd-7840-b05a-7855909d666b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PolicyholderAccountBalanceGuaranteedMinimumCreditRating_019d8775-5dfd-75f0-84cd-9660245cf65d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PolicyholderAccountBalanceGuaranteedMinimumCreditRating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PolicyholderAccountBalanceGuaranteedMinimumCreditingRateLineItems_019d8775-5dfd-7458-b466-86914e9b873f" xlink:to="loc_us-gaap_PolicyholderAccountBalanceGuaranteedMinimumCreditRating_019d8775-5dfd-75f0-84cd-9660245cf65d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_PolicyholderAccountBalanceBeforeReservesInExcessOfAccountBalance_019d8775-5dfd-7b2b-b322-11936ae1981d" xlink:href="unm-20260331.xsd#unm_PolicyholderAccountBalanceBeforeReservesInExcessOfAccountBalance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PolicyholderAccountBalanceGuaranteedMinimumCreditingRateLineItems_019d8775-5dfd-7458-b466-86914e9b873f" xlink:to="loc_unm_PolicyholderAccountBalanceBeforeReservesInExcessOfAccountBalance_019d8775-5dfd-7b2b-b322-11936ae1981d" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.unum.com/role/DeferredPolicyAcquisitionCostsDetails" xlink:type="simple" xlink:href="unm-20260331.xsd#DeferredPolicyAcquisitionCostsDetails"/>
  <link:definitionLink xlink:role="http://www.unum.com/role/DeferredPolicyAcquisitionCostsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredPolicyAcquisitionCostLineItems_019d8775-5dfd-773d-a823-45c9125beaa6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredPolicyAcquisitionCostLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredPolicyAcquisitionCostTable_019d8775-5dfd-7273-b882-c0efd13c4bce" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredPolicyAcquisitionCostTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DeferredPolicyAcquisitionCostLineItems_019d8775-5dfd-773d-a823-45c9125beaa6" xlink:to="loc_us-gaap_DeferredPolicyAcquisitionCostTable_019d8775-5dfd-7273-b882-c0efd13c4bce" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_019d8775-5dfd-7879-8172-cad0c273a5a5" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DeferredPolicyAcquisitionCostTable_019d8775-5dfd-7273-b882-c0efd13c4bce" xlink:to="loc_srt_ProductOrServiceAxis_019d8775-5dfd-7879-8172-cad0c273a5a5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019d8775-5dfd-7879-8172-cad0c273a5a5_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_019d8775-5dfd-7879-8172-cad0c273a5a5" xlink:to="loc_srt_ProductsAndServicesDomain_019d8775-5dfd-7879-8172-cad0c273a5a5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019d8775-5dfd-766a-a353-d6dcce649c64" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_019d8775-5dfd-7879-8172-cad0c273a5a5" xlink:to="loc_srt_ProductsAndServicesDomain_019d8775-5dfd-766a-a353-d6dcce649c64" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_GroupDisabilityMember_019d8775-5dfd-79a1-8034-15ed4f044d34" xlink:href="unm-20260331.xsd#unm_GroupDisabilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019d8775-5dfd-766a-a353-d6dcce649c64" xlink:to="loc_unm_GroupDisabilityMember_019d8775-5dfd-79a1-8034-15ed4f044d34" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_GroupLifeAndADDMember_019d8775-5dfd-797c-9739-d33b1f0e7714" xlink:href="unm-20260331.xsd#unm_GroupLifeAndADDMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019d8775-5dfd-766a-a353-d6dcce649c64" xlink:to="loc_unm_GroupLifeAndADDMember_019d8775-5dfd-797c-9739-d33b1f0e7714" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_VoluntaryBenefitsMember_019d8775-5dfd-7aa4-b6fb-18e0865c2f83" xlink:href="unm-20260331.xsd#unm_VoluntaryBenefitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019d8775-5dfd-766a-a353-d6dcce649c64" xlink:to="loc_unm_VoluntaryBenefitsMember_019d8775-5dfd-7aa4-b6fb-18e0865c2f83" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_IndividualDisabilityMember_019d8775-5dfd-71cf-8608-c84829545f5f" xlink:href="unm-20260331.xsd#unm_IndividualDisabilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019d8775-5dfd-766a-a353-d6dcce649c64" xlink:to="loc_unm_IndividualDisabilityMember_019d8775-5dfd-71cf-8608-c84829545f5f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_DentalandVisionMember_019d8775-5dfd-7078-af31-2d7421d469ca" xlink:href="unm-20260331.xsd#unm_DentalandVisionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019d8775-5dfd-766a-a353-d6dcce649c64" xlink:to="loc_unm_DentalandVisionMember_019d8775-5dfd-7078-af31-2d7421d469ca" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019d8775-5dfd-7bda-b2dd-e7845c4accfe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DeferredPolicyAcquisitionCostTable_019d8775-5dfd-7273-b882-c0efd13c4bce" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019d8775-5dfd-7bda-b2dd-e7845c4accfe" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019d8775-5dfd-7bda-b2dd-e7845c4accfe_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019d8775-5dfd-7bda-b2dd-e7845c4accfe" xlink:to="loc_us-gaap_SegmentDomain_019d8775-5dfd-7bda-b2dd-e7845c4accfe_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019d8775-5dfd-72e5-97c7-a6670c2fd84b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019d8775-5dfd-7bda-b2dd-e7845c4accfe" xlink:to="loc_us-gaap_SegmentDomain_019d8775-5dfd-72e5-97c7-a6670c2fd84b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_UnumUsMember_019d8775-5dfd-7097-b6e0-07801ddca194" xlink:href="unm-20260331.xsd#unm_UnumUsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019d8775-5dfd-72e5-97c7-a6670c2fd84b" xlink:to="loc_unm_UnumUsMember_019d8775-5dfd-7097-b6e0-07801ddca194" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_UnumInternationalMember_019d8775-5dfd-7f28-ab00-7405efcaf939" xlink:href="unm-20260331.xsd#unm_UnumInternationalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019d8775-5dfd-72e5-97c7-a6670c2fd84b" xlink:to="loc_unm_UnumInternationalMember_019d8775-5dfd-7f28-ab00-7405efcaf939" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_ColonialLifeMember_019d8775-5dfd-7d74-a9d5-4274eff3c051" xlink:href="unm-20260331.xsd#unm_ColonialLifeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019d8775-5dfd-72e5-97c7-a6670c2fd84b" xlink:to="loc_unm_ColonialLifeMember_019d8775-5dfd-7d74-a9d5-4274eff3c051" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_019d8775-5dfd-7a96-8129-087519caf9f0" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DeferredPolicyAcquisitionCostTable_019d8775-5dfd-7273-b882-c0efd13c4bce" xlink:to="loc_srt_ConsolidationItemsAxis_019d8775-5dfd-7a96-8129-087519caf9f0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019d8775-5dfd-7a96-8129-087519caf9f0_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_019d8775-5dfd-7a96-8129-087519caf9f0" xlink:to="loc_srt_ConsolidationItemsDomain_019d8775-5dfd-7a96-8129-087519caf9f0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019d8775-5dfd-7b02-b917-2ababb81d4f0" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_019d8775-5dfd-7a96-8129-087519caf9f0" xlink:to="loc_srt_ConsolidationItemsDomain_019d8775-5dfd-7b02-b917-2ababb81d4f0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_019d8775-5dfd-74b5-8c92-1ce8a3c2db18" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_019d8775-5dfd-7b02-b917-2ababb81d4f0" xlink:to="loc_us-gaap_OperatingSegmentsMember_019d8775-5dfd-74b5-8c92-1ce8a3c2db18" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MovementAnalysisOfDeferredPolicyAcquisitionCostsRollForward_019d8775-5dfd-7504-8f3e-7cdb1b9559ea" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MovementAnalysisOfDeferredPolicyAcquisitionCostsRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DeferredPolicyAcquisitionCostLineItems_019d8775-5dfd-773d-a823-45c9125beaa6" xlink:to="loc_us-gaap_MovementAnalysisOfDeferredPolicyAcquisitionCostsRollForward_019d8775-5dfd-7504-8f3e-7cdb1b9559ea" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredPolicyAcquisitionCosts_019d8775-5dfd-75df-a8ab-3c323bdc511a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredPolicyAcquisitionCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MovementAnalysisOfDeferredPolicyAcquisitionCostsRollForward_019d8775-5dfd-7504-8f3e-7cdb1b9559ea" xlink:to="loc_us-gaap_DeferredPolicyAcquisitionCosts_019d8775-5dfd-75df-a8ab-3c323bdc511a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredPolicyAcquisitionCostsAdditions_019d8775-5dfd-723a-8d4e-5213eb4f5c4e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredPolicyAcquisitionCostsAdditions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MovementAnalysisOfDeferredPolicyAcquisitionCostsRollForward_019d8775-5dfd-7504-8f3e-7cdb1b9559ea" xlink:to="loc_us-gaap_DeferredPolicyAcquisitionCostsAdditions_019d8775-5dfd-723a-8d4e-5213eb4f5c4e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredPolicyAcquisitionCostAmortizationExpense_019d8775-5dfd-78d7-917a-273bcfe4fc9d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredPolicyAcquisitionCostAmortizationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MovementAnalysisOfDeferredPolicyAcquisitionCostsRollForward_019d8775-5dfd-7504-8f3e-7cdb1b9559ea" xlink:to="loc_us-gaap_DeferredPolicyAcquisitionCostAmortizationExpense_019d8775-5dfd-78d7-917a-273bcfe4fc9d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredPolicyAcquisitionCostForeignCurrencyTranslationAdjustmentAndOther_019d8775-5dfd-74e0-b448-6d983e61a7b7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredPolicyAcquisitionCostForeignCurrencyTranslationAdjustmentAndOther"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MovementAnalysisOfDeferredPolicyAcquisitionCostsRollForward_019d8775-5dfd-7504-8f3e-7cdb1b9559ea" xlink:to="loc_us-gaap_DeferredPolicyAcquisitionCostForeignCurrencyTranslationAdjustmentAndOther_019d8775-5dfd-74e0-b448-6d983e61a7b7" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredPolicyAcquisitionCosts_019d8775-5dfd-7e40-9e63-b0bbb453bd55" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredPolicyAcquisitionCosts"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.unum.com/role/PremiumIncomebyMajorLineofBusinesswithinEachSegmentDetail" xlink:type="simple" xlink:href="unm-20260331.xsd#PremiumIncomebyMajorLineofBusinesswithinEachSegmentDetail"/>
  <link:definitionLink xlink:role="http://www.unum.com/role/PremiumIncomebyMajorLineofBusinesswithinEachSegmentDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_019d8775-5dfd-7649-a763-13567aa95c0b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019d8775-5dfd-7849-91ae-e795a08076cc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019d8775-5dfd-7649-a763-13567aa95c0b" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019d8775-5dfd-7849-91ae-e795a08076cc" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_019d8775-5dfd-7d14-bbd7-1c2ef5351900" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019d8775-5dfd-7849-91ae-e795a08076cc" xlink:to="loc_srt_ConsolidationItemsAxis_019d8775-5dfd-7d14-bbd7-1c2ef5351900" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019d8775-5dfd-7d14-bbd7-1c2ef5351900_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_019d8775-5dfd-7d14-bbd7-1c2ef5351900" xlink:to="loc_srt_ConsolidationItemsDomain_019d8775-5dfd-7d14-bbd7-1c2ef5351900_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019d8775-5dfd-7a47-bde5-c3e2dcdecefe" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_019d8775-5dfd-7d14-bbd7-1c2ef5351900" xlink:to="loc_srt_ConsolidationItemsDomain_019d8775-5dfd-7a47-bde5-c3e2dcdecefe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_019d8775-5dfd-7e2f-8d47-39a144c497c9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_019d8775-5dfd-7a47-bde5-c3e2dcdecefe" xlink:to="loc_us-gaap_OperatingSegmentsMember_019d8775-5dfd-7e2f-8d47-39a144c497c9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019d8775-5dfd-7b37-841b-c0707c88e5b0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019d8775-5dfd-7849-91ae-e795a08076cc" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019d8775-5dfd-7b37-841b-c0707c88e5b0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019d8775-5dfd-7b37-841b-c0707c88e5b0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019d8775-5dfd-7b37-841b-c0707c88e5b0" xlink:to="loc_us-gaap_SegmentDomain_019d8775-5dfd-7b37-841b-c0707c88e5b0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019d8775-5dfd-7237-b6cb-445bda4997d1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019d8775-5dfd-7b37-841b-c0707c88e5b0" xlink:to="loc_us-gaap_SegmentDomain_019d8775-5dfd-7237-b6cb-445bda4997d1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_UnumUsMember_019d8775-5dfd-7491-aa13-54ea6076ee68" xlink:href="unm-20260331.xsd#unm_UnumUsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019d8775-5dfd-7237-b6cb-445bda4997d1" xlink:to="loc_unm_UnumUsMember_019d8775-5dfd-7491-aa13-54ea6076ee68" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_UnumInternationalMember_019d8775-5dfd-7d9f-8409-24a987f68a86" xlink:href="unm-20260331.xsd#unm_UnumInternationalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019d8775-5dfd-7237-b6cb-445bda4997d1" xlink:to="loc_unm_UnumInternationalMember_019d8775-5dfd-7d9f-8409-24a987f68a86" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_ColonialLifeMember_019d8775-5dfd-769e-a3e7-a4c4dbaad138" xlink:href="unm-20260331.xsd#unm_ColonialLifeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019d8775-5dfd-7237-b6cb-445bda4997d1" xlink:to="loc_unm_ColonialLifeMember_019d8775-5dfd-769e-a3e7-a4c4dbaad138" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_ClosedBlockMember_019d8775-5dfd-74e6-a7e7-31aa99bae4fe" xlink:href="unm-20260331.xsd#unm_ClosedBlockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019d8775-5dfd-7237-b6cb-445bda4997d1" xlink:to="loc_unm_ClosedBlockMember_019d8775-5dfd-74e6-a7e7-31aa99bae4fe" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_019d8775-5dfd-71ad-8819-bd26f01f01bc" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019d8775-5dfd-7849-91ae-e795a08076cc" xlink:to="loc_srt_ProductOrServiceAxis_019d8775-5dfd-71ad-8819-bd26f01f01bc" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019d8775-5dfd-71ad-8819-bd26f01f01bc_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_019d8775-5dfd-71ad-8819-bd26f01f01bc" xlink:to="loc_srt_ProductsAndServicesDomain_019d8775-5dfd-71ad-8819-bd26f01f01bc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019d8775-5dfd-7069-b37b-4a6a863d0ff3" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_019d8775-5dfd-71ad-8819-bd26f01f01bc" xlink:to="loc_srt_ProductsAndServicesDomain_019d8775-5dfd-7069-b37b-4a6a863d0ff3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_GroupLongTermDisabilityMember_019d8775-5dfd-7ca0-876b-949fba44a543" xlink:href="unm-20260331.xsd#unm_GroupLongTermDisabilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019d8775-5dfd-7069-b37b-4a6a863d0ff3" xlink:to="loc_unm_GroupLongTermDisabilityMember_019d8775-5dfd-7ca0-876b-949fba44a543" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_GroupShortTermDisabilityMember_019d8775-5dfd-7ad2-810a-0a68dd226caa" xlink:href="unm-20260331.xsd#unm_GroupShortTermDisabilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019d8775-5dfd-7069-b37b-4a6a863d0ff3" xlink:to="loc_unm_GroupShortTermDisabilityMember_019d8775-5dfd-7ad2-810a-0a68dd226caa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_GroupLifeMember_019d8775-5dfd-7db3-a42c-3611c5f7ab00" xlink:href="unm-20260331.xsd#unm_GroupLifeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019d8775-5dfd-7069-b37b-4a6a863d0ff3" xlink:to="loc_unm_GroupLifeMember_019d8775-5dfd-7db3-a42c-3611c5f7ab00" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_AccidentalDeathDismembermentMember_019d8775-5dfd-7aa4-8917-39d4643d0b45" xlink:href="unm-20260331.xsd#unm_AccidentalDeathDismembermentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019d8775-5dfd-7069-b37b-4a6a863d0ff3" xlink:to="loc_unm_AccidentalDeathDismembermentMember_019d8775-5dfd-7aa4-8917-39d4643d0b45" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_VoluntaryBenefitsMember_019d8775-5dfd-7d7f-afb1-8f528e039deb" xlink:href="unm-20260331.xsd#unm_VoluntaryBenefitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019d8775-5dfd-7069-b37b-4a6a863d0ff3" xlink:to="loc_unm_VoluntaryBenefitsMember_019d8775-5dfd-7d7f-afb1-8f528e039deb" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_IndividualDisabilityMember_019d8775-5dfd-7e95-97bc-45f65d74fb00" xlink:href="unm-20260331.xsd#unm_IndividualDisabilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019d8775-5dfd-7069-b37b-4a6a863d0ff3" xlink:to="loc_unm_IndividualDisabilityMember_019d8775-5dfd-7e95-97bc-45f65d74fb00" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_DentalandVisionMember_019d8775-5dfd-78ff-a32f-db7800e18fec" xlink:href="unm-20260331.xsd#unm_DentalandVisionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019d8775-5dfd-7069-b37b-4a6a863d0ff3" xlink:to="loc_unm_DentalandVisionMember_019d8775-5dfd-78ff-a32f-db7800e18fec" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_SupplementalandVoluntaryInsuranceMember_019d8775-5dfd-7376-8b5b-1321dd398423" xlink:href="unm-20260331.xsd#unm_SupplementalandVoluntaryInsuranceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019d8775-5dfd-7069-b37b-4a6a863d0ff3" xlink:to="loc_unm_SupplementalandVoluntaryInsuranceMember_019d8775-5dfd-7376-8b5b-1321dd398423" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_UnumPolandMember_019d8775-5dfd-7cf0-aa0a-e5232d01168a" xlink:href="unm-20260331.xsd#unm_UnumPolandMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019d8775-5dfd-7069-b37b-4a6a863d0ff3" xlink:to="loc_unm_UnumPolandMember_019d8775-5dfd-7cf0-aa0a-e5232d01168a" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccidentAndHealthInsuranceSegmentMember_019d8775-5dfd-7cd7-8d40-0695f8380dbf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccidentAndHealthInsuranceSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019d8775-5dfd-7069-b37b-4a6a863d0ff3" xlink:to="loc_us-gaap_AccidentAndHealthInsuranceSegmentMember_019d8775-5dfd-7cd7-8d40-0695f8380dbf" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LifeInsuranceSegmentMember_019d8775-5dfd-78f9-9f9f-409e4eb70d00" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LifeInsuranceSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019d8775-5dfd-7069-b37b-4a6a863d0ff3" xlink:to="loc_us-gaap_LifeInsuranceSegmentMember_019d8775-5dfd-78f9-9f9f-409e4eb70d00" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_CancerAndCriticalIllnessColonialMember_019d8775-5dfd-77d8-a7bc-0d319cda73c1" xlink:href="unm-20260331.xsd#unm_CancerAndCriticalIllnessColonialMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019d8775-5dfd-7069-b37b-4a6a863d0ff3" xlink:to="loc_unm_CancerAndCriticalIllnessColonialMember_019d8775-5dfd-77d8-a7bc-0d319cda73c1" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_LongTermCareMember_019d8775-5dfd-7f64-893c-101412d8f646" xlink:href="unm-20260331.xsd#unm_LongTermCareMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019d8775-5dfd-7069-b37b-4a6a863d0ff3" xlink:to="loc_unm_LongTermCareMember_019d8775-5dfd-7f64-893c-101412d8f646" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherInsuranceProductLineMember_019d8775-5dfd-7719-bcb6-602bef086eee" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherInsuranceProductLineMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019d8775-5dfd-7069-b37b-4a6a863d0ff3" xlink:to="loc_us-gaap_OtherInsuranceProductLineMember_019d8775-5dfd-7719-bcb6-602bef086eee" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PremiumsEarnedNet_019d8775-5dfd-793c-a8e5-ecc094471b24" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PremiumsEarnedNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019d8775-5dfd-7649-a763-13567aa95c0b" xlink:to="loc_us-gaap_PremiumsEarnedNet_019d8775-5dfd-793c-a8e5-ecc094471b24" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.unum.com/role/SelectedOperatingStatementDatabySegmentDetail" xlink:type="simple" xlink:href="unm-20260331.xsd#SelectedOperatingStatementDatabySegmentDetail"/>
  <link:definitionLink xlink:role="http://www.unum.com/role/SelectedOperatingStatementDatabySegmentDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_019d8775-5dfd-702a-a375-4924237cf84e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019d8775-5dfd-7429-82d0-9dd33607bd50" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019d8775-5dfd-702a-a375-4924237cf84e" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019d8775-5dfd-7429-82d0-9dd33607bd50" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_019d8775-5dfd-760d-8c50-f2aacd15d2e5" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019d8775-5dfd-7429-82d0-9dd33607bd50" xlink:to="loc_srt_ConsolidationItemsAxis_019d8775-5dfd-760d-8c50-f2aacd15d2e5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019d8775-5dfd-760d-8c50-f2aacd15d2e5_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_019d8775-5dfd-760d-8c50-f2aacd15d2e5" xlink:to="loc_srt_ConsolidationItemsDomain_019d8775-5dfd-760d-8c50-f2aacd15d2e5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019d8775-5dfd-7c87-a267-8dc239fd94e9" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_019d8775-5dfd-760d-8c50-f2aacd15d2e5" xlink:to="loc_srt_ConsolidationItemsDomain_019d8775-5dfd-7c87-a267-8dc239fd94e9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_019d8775-5dfd-752c-92fa-25b451f64742" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_019d8775-5dfd-7c87-a267-8dc239fd94e9" xlink:to="loc_us-gaap_OperatingSegmentsMember_019d8775-5dfd-752c-92fa-25b451f64742" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019d8775-5dfd-7e7a-a3df-0e8d11001242" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019d8775-5dfd-7429-82d0-9dd33607bd50" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019d8775-5dfd-7e7a-a3df-0e8d11001242" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019d8775-5dfd-7e7a-a3df-0e8d11001242_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019d8775-5dfd-7e7a-a3df-0e8d11001242" xlink:to="loc_us-gaap_SegmentDomain_019d8775-5dfd-7e7a-a3df-0e8d11001242_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019d8775-5dfd-7634-8ebf-086f0787e75b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019d8775-5dfd-7e7a-a3df-0e8d11001242" xlink:to="loc_us-gaap_SegmentDomain_019d8775-5dfd-7634-8ebf-086f0787e75b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_UnumUsMember_019d8775-5dfd-7b0d-914c-8378299ca3ba" xlink:href="unm-20260331.xsd#unm_UnumUsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019d8775-5dfd-7634-8ebf-086f0787e75b" xlink:to="loc_unm_UnumUsMember_019d8775-5dfd-7b0d-914c-8378299ca3ba" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_UnumInternationalMember_019d8775-5dfd-73bc-923f-a47dda6bd8b2" xlink:href="unm-20260331.xsd#unm_UnumInternationalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019d8775-5dfd-7634-8ebf-086f0787e75b" xlink:to="loc_unm_UnumInternationalMember_019d8775-5dfd-73bc-923f-a47dda6bd8b2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_ColonialLifeMember_019d8775-5dfd-7f41-9f5f-bf59766a57ed" xlink:href="unm-20260331.xsd#unm_ColonialLifeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019d8775-5dfd-7634-8ebf-086f0787e75b" xlink:to="loc_unm_ColonialLifeMember_019d8775-5dfd-7f41-9f5f-bf59766a57ed" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_ClosedBlockMember_019d8775-5dfd-7eae-a756-520ca3846fb7" xlink:href="unm-20260331.xsd#unm_ClosedBlockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019d8775-5dfd-7634-8ebf-086f0787e75b" xlink:to="loc_unm_ClosedBlockMember_019d8775-5dfd-7eae-a756-520ca3846fb7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateAndOtherMember_019d8775-5dfd-7a26-b91b-f49e4606074d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CorporateAndOtherMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019d8775-5dfd-7634-8ebf-086f0787e75b" xlink:to="loc_us-gaap_CorporateAndOtherMember_019d8775-5dfd-7a26-b91b-f49e4606074d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PremiumsEarnedNet_019d8775-5dfd-71a8-942c-696422f15484" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PremiumsEarnedNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019d8775-5dfd-702a-a375-4924237cf84e" xlink:to="loc_us-gaap_PremiumsEarnedNet_019d8775-5dfd-71a8-942c-696422f15484" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetInvestmentIncome_019d8775-5dfd-71b0-9c3b-b677b085c900" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetInvestmentIncome"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019d8775-5dfd-702a-a375-4924237cf84e" xlink:to="loc_us-gaap_NetInvestmentIncome_019d8775-5dfd-71b0-9c3b-b677b085c900" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherIncome_019d8775-5dfd-79cf-9098-caa284232939" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherIncome"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019d8775-5dfd-702a-a375-4924237cf84e" xlink:to="loc_us-gaap_OtherIncome_019d8775-5dfd-79cf-9098-caa284232939" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_SegmentAdjustedOperatingRevenue_019d8775-5dfd-73be-b343-b68c33f010d4" xlink:href="unm-20260331.xsd#unm_SegmentAdjustedOperatingRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019d8775-5dfd-702a-a375-4924237cf84e" xlink:to="loc_unm_SegmentAdjustedOperatingRevenue_019d8775-5dfd-73be-b343-b68c33f010d4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PolicyholderBenefitsAndClaimsIncurredNet_019dc1cd-7c30-7749-aa31-dad565ce9602" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PolicyholderBenefitsAndClaimsIncurredNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019d8775-5dfd-702a-a375-4924237cf84e" xlink:to="loc_us-gaap_PolicyholderBenefitsAndClaimsIncurredNet_019dc1cd-7c30-7749-aa31-dad565ce9602" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForFuturePolicyBenefitRemeasurementGainLoss_019dc1cd-d7f4-77a3-8cb7-cfad2e9cc72d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilityForFuturePolicyBenefitRemeasurementGainLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019d8775-5dfd-702a-a375-4924237cf84e" xlink:to="loc_us-gaap_LiabilityForFuturePolicyBenefitRemeasurementGainLoss_019dc1cd-d7f4-77a3-8cb7-cfad2e9cc72d" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InsuranceCommissions_019d8775-5dfd-79eb-b20d-bcf28af53d4a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InsuranceCommissions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019d8775-5dfd-702a-a375-4924237cf84e" xlink:to="loc_us-gaap_InsuranceCommissions_019d8775-5dfd-79eb-b20d-bcf28af53d4a" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestAndDebtExpense_019d8775-5dfd-7f40-b95d-c87a96b3180d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestAndDebtExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019d8775-5dfd-702a-a375-4924237cf84e" xlink:to="loc_us-gaap_InterestAndDebtExpense_019d8775-5dfd-7f40-b95d-c87a96b3180d" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_DeferralOfAcquisitionCosts_019d8775-5dfd-757e-9332-e8cf721f0db5" xlink:href="unm-20260331.xsd#unm_DeferralOfAcquisitionCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019d8775-5dfd-702a-a375-4924237cf84e" xlink:to="loc_unm_DeferralOfAcquisitionCosts_019d8775-5dfd-757e-9332-e8cf721f0db5" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredPolicyAcquisitionCostAmortizationExpense_019d8775-5dfd-74ae-8c00-a3a0c05a5d24" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredPolicyAcquisitionCostAmortizationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019d8775-5dfd-702a-a375-4924237cf84e" xlink:to="loc_us-gaap_DeferredPolicyAcquisitionCostAmortizationExpense_019d8775-5dfd-74ae-8c00-a3a0c05a5d24" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BenefitsLossesAndExpenses_019dc1d0-d082-7155-abc7-17b9907fef62" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BenefitsLossesAndExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019d8775-5dfd-702a-a375-4924237cf84e" xlink:to="loc_us-gaap_BenefitsLossesAndExpenses_019dc1d0-d082-7155-abc7-17b9907fef62" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_019d8775-5dfd-7c0e-b274-99646939170a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019d8775-5dfd-702a-a375-4924237cf84e" xlink:to="loc_us-gaap_OperatingIncomeLoss_019d8775-5dfd-7c0e-b274-99646939170a" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingOtherItemAmount_019d8775-5dfd-7f75-ac15-3c1a838c2ab3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingOtherItemAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019d8775-5dfd-702a-a375-4924237cf84e" xlink:to="loc_us-gaap_SegmentReportingOtherItemAmount_019d8775-5dfd-7f75-ac15-3c1a838c2ab3" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepreciationDepletionAndAmortization_019d8775-5dfd-73ba-a174-08eb692c2150" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DepreciationDepletionAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingOtherItemAmount_019d8775-5dfd-7f75-ac15-3c1a838c2ab3" xlink:to="loc_us-gaap_DepreciationDepletionAndAmortization_019d8775-5dfd-73ba-a174-08eb692c2150" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.unum.com/role/AssetsbySegmentDetail" xlink:type="simple" xlink:href="unm-20260331.xsd#AssetsbySegmentDetail"/>
  <link:definitionLink xlink:role="http://www.unum.com/role/AssetsbySegmentDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_019d8775-5dfd-7ba8-9371-426ed8883d12" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019d8775-5dfd-7a96-909f-1f67d2bff2d0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019d8775-5dfd-7ba8-9371-426ed8883d12" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019d8775-5dfd-7a96-909f-1f67d2bff2d0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_019d8775-5dfd-7977-852c-148c277b9870" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019d8775-5dfd-7a96-909f-1f67d2bff2d0" xlink:to="loc_srt_ConsolidationItemsAxis_019d8775-5dfd-7977-852c-148c277b9870" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019d8775-5dfd-7977-852c-148c277b9870_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_019d8775-5dfd-7977-852c-148c277b9870" xlink:to="loc_srt_ConsolidationItemsDomain_019d8775-5dfd-7977-852c-148c277b9870_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019d8775-5dfd-7c8a-b5ad-c858e07f1dbc" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_019d8775-5dfd-7977-852c-148c277b9870" xlink:to="loc_srt_ConsolidationItemsDomain_019d8775-5dfd-7c8a-b5ad-c858e07f1dbc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_019d8775-5dfd-79b1-b04b-cd5a40c15c92" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_019d8775-5dfd-7c8a-b5ad-c858e07f1dbc" xlink:to="loc_us-gaap_OperatingSegmentsMember_019d8775-5dfd-79b1-b04b-cd5a40c15c92" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019d8775-5dfd-796e-9053-a1984c6238d7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019d8775-5dfd-7a96-909f-1f67d2bff2d0" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019d8775-5dfd-796e-9053-a1984c6238d7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019d8775-5dfd-796e-9053-a1984c6238d7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019d8775-5dfd-796e-9053-a1984c6238d7" xlink:to="loc_us-gaap_SegmentDomain_019d8775-5dfd-796e-9053-a1984c6238d7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019d8775-5dfd-7e3f-9f6b-1e16592665e1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019d8775-5dfd-796e-9053-a1984c6238d7" xlink:to="loc_us-gaap_SegmentDomain_019d8775-5dfd-7e3f-9f6b-1e16592665e1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_UnumUsMember_019d8775-5dfd-75c2-83e9-58ea52539f42" xlink:href="unm-20260331.xsd#unm_UnumUsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019d8775-5dfd-7e3f-9f6b-1e16592665e1" xlink:to="loc_unm_UnumUsMember_019d8775-5dfd-75c2-83e9-58ea52539f42" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_UnumInternationalMember_019d8775-5dfd-7512-bd3d-a73baed49fb5" xlink:href="unm-20260331.xsd#unm_UnumInternationalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019d8775-5dfd-7e3f-9f6b-1e16592665e1" xlink:to="loc_unm_UnumInternationalMember_019d8775-5dfd-7512-bd3d-a73baed49fb5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_ColonialLifeMember_019d8775-5dfd-72ad-b091-6e5cf8a8559d" xlink:href="unm-20260331.xsd#unm_ColonialLifeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019d8775-5dfd-7e3f-9f6b-1e16592665e1" xlink:to="loc_unm_ColonialLifeMember_019d8775-5dfd-72ad-b091-6e5cf8a8559d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_ClosedBlockMember_019d8775-5dfd-7e94-a922-7086a22efd20" xlink:href="unm-20260331.xsd#unm_ClosedBlockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019d8775-5dfd-7e3f-9f6b-1e16592665e1" xlink:to="loc_unm_ClosedBlockMember_019d8775-5dfd-7e94-a922-7086a22efd20" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateAndOtherMember_019d8775-5dfd-7d0a-9f82-5012a4cbfae4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CorporateAndOtherMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019d8775-5dfd-7e3f-9f6b-1e16592665e1" xlink:to="loc_us-gaap_CorporateAndOtherMember_019d8775-5dfd-7d0a-9f82-5012a4cbfae4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_019d8775-5dfd-7a0f-a417-09d7af4e5cec" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Assets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019d8775-5dfd-7ba8-9371-426ed8883d12" xlink:to="loc_us-gaap_Assets_019d8775-5dfd-7a0f-a417-09d7af4e5cec" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.unum.com/role/ReconciliationofTotalRevenueandIncomeBeforeIncomeTaxtoOperatingRevenueandSegmentAdjustedOperatingIncomeDetail" xlink:type="simple" xlink:href="unm-20260331.xsd#ReconciliationofTotalRevenueandIncomeBeforeIncomeTaxtoOperatingRevenueandSegmentAdjustedOperatingIncomeDetail"/>
  <link:definitionLink xlink:role="http://www.unum.com/role/ReconciliationofTotalRevenueandIncomeBeforeIncomeTaxtoOperatingRevenueandSegmentAdjustedOperatingIncomeDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_019d8775-5dfd-78ea-b2b6-acedfd241026" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019d8775-5dfd-7e7d-901f-86dd2ed2aad2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019d8775-5dfd-78ea-b2b6-acedfd241026" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019d8775-5dfd-7e7d-901f-86dd2ed2aad2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_019d8775-5dfd-7fca-8a49-3f56849ffb4a" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019d8775-5dfd-7e7d-901f-86dd2ed2aad2" xlink:to="loc_srt_ConsolidationItemsAxis_019d8775-5dfd-7fca-8a49-3f56849ffb4a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019d8775-5dfd-7fca-8a49-3f56849ffb4a_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_019d8775-5dfd-7fca-8a49-3f56849ffb4a" xlink:to="loc_srt_ConsolidationItemsDomain_019d8775-5dfd-7fca-8a49-3f56849ffb4a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019d8775-5dfd-7074-a967-3eda5cd351f6" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_019d8775-5dfd-7fca-8a49-3f56849ffb4a" xlink:to="loc_srt_ConsolidationItemsDomain_019d8775-5dfd-7074-a967-3eda5cd351f6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_019d8775-5dfd-73f4-8be2-a4ccbc51cede" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_019d8775-5dfd-7074-a967-3eda5cd351f6" xlink:to="loc_us-gaap_OperatingSegmentsMember_019d8775-5dfd-73f4-8be2-a4ccbc51cede" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_SignificantTransactionAxis_019d8775-5dfd-76fc-92fd-29442389279a" xlink:href="unm-20260331.xsd#unm_SignificantTransactionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019d8775-5dfd-7e7d-901f-86dd2ed2aad2" xlink:to="loc_unm_SignificantTransactionAxis_019d8775-5dfd-76fc-92fd-29442389279a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_SignificantTransactionDomain_019d8775-5dfd-76fc-92fd-29442389279a_default" xlink:href="unm-20260331.xsd#unm_SignificantTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_unm_SignificantTransactionAxis_019d8775-5dfd-76fc-92fd-29442389279a" xlink:to="loc_unm_SignificantTransactionDomain_019d8775-5dfd-76fc-92fd-29442389279a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_SignificantTransactionDomain_019d8775-5dfd-7eb1-bd5b-e66b1a28ef73" xlink:href="unm-20260331.xsd#unm_SignificantTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_unm_SignificantTransactionAxis_019d8775-5dfd-76fc-92fd-29442389279a" xlink:to="loc_unm_SignificantTransactionDomain_019d8775-5dfd-7eb1-bd5b-e66b1a28ef73" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_LongTermCareAndIndividualDisabilityReinsuranceTransactionMember_019d8775-5dfd-7429-b2e4-5cb7276c4811" xlink:href="unm-20260331.xsd#unm_LongTermCareAndIndividualDisabilityReinsuranceTransactionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_unm_SignificantTransactionDomain_019d8775-5dfd-7eb1-bd5b-e66b1a28ef73" xlink:to="loc_unm_LongTermCareAndIndividualDisabilityReinsuranceTransactionMember_019d8775-5dfd-7429-b2e4-5cb7276c4811" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_UnrelatedToSignificantTransactionMember_019d8775-5dfd-7359-9fdd-37ed0b1c8d65" xlink:href="unm-20260331.xsd#unm_UnrelatedToSignificantTransactionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_unm_SignificantTransactionDomain_019d8775-5dfd-7eb1-bd5b-e66b1a28ef73" xlink:to="loc_unm_UnrelatedToSignificantTransactionMember_019d8775-5dfd-7359-9fdd-37ed0b1c8d65" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_019d8775-5dfd-7c5e-8432-1bf5cd5a0ea9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Revenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019d8775-5dfd-78ea-b2b6-acedfd241026" xlink:to="loc_us-gaap_Revenues_019d8775-5dfd-7c5e-8432-1bf5cd5a0ea9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnInvestments_019d8775-5dfd-7393-91b1-a5a3940d0627" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainLossOnInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019d8775-5dfd-78ea-b2b6-acedfd241026" xlink:to="loc_us-gaap_GainLossOnInvestments_019d8775-5dfd-7393-91b1-a5a3940d0627" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_SegmentAdjustedOperatingRevenue_019d8775-5dfd-74bd-9255-d16f14642697" xlink:href="unm-20260331.xsd#unm_SegmentAdjustedOperatingRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019d8775-5dfd-78ea-b2b6-acedfd241026" xlink:to="loc_unm_SegmentAdjustedOperatingRevenue_019d8775-5dfd-74bd-9255-d16f14642697" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments_019d8775-5dfd-78b0-8587-120f47490eae" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019d8775-5dfd-78ea-b2b6-acedfd241026" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments_019d8775-5dfd-78b0-8587-120f47490eae" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_019d8775-5dfd-7dcb-92fe-15c2f2824f25" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019d8775-5dfd-78ea-b2b6-acedfd241026" xlink:to="loc_us-gaap_OperatingIncomeLoss_019d8775-5dfd-7dcb-92fe-15c2f2824f25" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.unum.com/role/SegmentInformationSegmentsAdditionalInformationDetail" xlink:type="simple" xlink:href="unm-20260331.xsd#SegmentInformationSegmentsAdditionalInformationDetail"/>
  <link:definitionLink xlink:role="http://www.unum.com/role/SegmentInformationSegmentsAdditionalInformationDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_019d8775-5dfd-73b6-80aa-5a40caf9b19f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019d8775-5dfd-7e06-ae5a-5ae229c9edde" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019d8775-5dfd-73b6-80aa-5a40caf9b19f" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019d8775-5dfd-7e06-ae5a-5ae229c9edde" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019d8775-5dfd-710b-8c0b-9fdec09b20ff" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019d8775-5dfd-7e06-ae5a-5ae229c9edde" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019d8775-5dfd-710b-8c0b-9fdec09b20ff" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019d8775-5dfd-710b-8c0b-9fdec09b20ff_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019d8775-5dfd-710b-8c0b-9fdec09b20ff" xlink:to="loc_us-gaap_SegmentDomain_019d8775-5dfd-710b-8c0b-9fdec09b20ff_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019d8775-5dfd-732d-a64a-50cfccc967f9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019d8775-5dfd-710b-8c0b-9fdec09b20ff" xlink:to="loc_us-gaap_SegmentDomain_019d8775-5dfd-732d-a64a-50cfccc967f9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_UnumUsMember_019d8775-5dfd-71fd-9f19-dda69a41789d" xlink:href="unm-20260331.xsd#unm_UnumUsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019d8775-5dfd-732d-a64a-50cfccc967f9" xlink:to="loc_unm_UnumUsMember_019d8775-5dfd-71fd-9f19-dda69a41789d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_ColonialLifeMember_019d8775-5dfd-73f2-bcfb-6c31bbc7696d" xlink:href="unm-20260331.xsd#unm_ColonialLifeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019d8775-5dfd-732d-a64a-50cfccc967f9" xlink:to="loc_unm_ColonialLifeMember_019d8775-5dfd-73f2-bcfb-6c31bbc7696d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_UnumInternationalMember_019d8775-5dfd-7962-974e-30b429aa5aca" xlink:href="unm-20260331.xsd#unm_UnumInternationalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019d8775-5dfd-732d-a64a-50cfccc967f9" xlink:to="loc_unm_UnumInternationalMember_019d8775-5dfd-7962-974e-30b429aa5aca" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_019d8775-5dfd-7586-b61b-55053da2bd87" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019d8775-5dfd-73b6-80aa-5a40caf9b19f" xlink:to="loc_us-gaap_Goodwill_019d8775-5dfd-7586-b61b-55053da2bd87" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfOperatingSegments_019d8775-5dfd-732d-a8be-434f11c2ad02" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NumberOfOperatingSegments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019d8775-5dfd-73b6-80aa-5a40caf9b19f" xlink:to="loc_us-gaap_NumberOfOperatingSegments_019d8775-5dfd-732d-a8be-434f11c2ad02" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.unum.com/role/EmployeeBenefitPlansNetPeriodicBenefitCostDetail" xlink:type="simple" xlink:href="unm-20260331.xsd#EmployeeBenefitPlansNetPeriodicBenefitCostDetail"/>
  <link:definitionLink xlink:role="http://www.unum.com/role/EmployeeBenefitPlansNetPeriodicBenefitCostDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansTableTextBlockLineItems_019d8775-5dfe-75cb-976b-4e8f1cb36fff" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansTableTextBlockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansDisclosuresTable_019d8775-5dfe-7965-80ca-504b45824fd4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansDisclosuresTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansTableTextBlockLineItems_019d8775-5dfe-75cb-976b-4e8f1cb36fff" xlink:to="loc_us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansDisclosuresTable_019d8775-5dfe-7965-80ca-504b45824fd4" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeAxis_019d8775-5dfe-72a1-af1e-2060dafffa03" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetirementPlanTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansDisclosuresTable_019d8775-5dfe-7965-80ca-504b45824fd4" xlink:to="loc_us-gaap_RetirementPlanTypeAxis_019d8775-5dfe-72a1-af1e-2060dafffa03" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_019d8775-5dfe-72a1-af1e-2060dafffa03_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetirementPlanTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RetirementPlanTypeAxis_019d8775-5dfe-72a1-af1e-2060dafffa03" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_019d8775-5dfe-72a1-af1e-2060dafffa03_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_019d8775-5dfe-7276-a896-2deb23fadbc3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetirementPlanTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RetirementPlanTypeAxis_019d8775-5dfe-72a1-af1e-2060dafffa03" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_019d8775-5dfe-7276-a896-2deb23fadbc3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PensionPlansDefinedBenefitMember_019d8775-5dfe-7845-94a9-ab377b6b7e99" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PensionPlansDefinedBenefitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanTypeDomain_019d8775-5dfe-7276-a896-2deb23fadbc3" xlink:to="loc_us-gaap_PensionPlansDefinedBenefitMember_019d8775-5dfe-7845-94a9-ab377b6b7e99" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember_019d8775-5dfe-759f-9f2f-25c08633cc88" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanTypeDomain_019d8775-5dfe-7276-a896-2deb23fadbc3" xlink:to="loc_us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember_019d8775-5dfe-759f-9f2f-25c08633cc88" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanSponsorLocationAxis_019d8775-5dfe-7e40-892a-eba545123604" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetirementPlanSponsorLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansDisclosuresTable_019d8775-5dfe-7965-80ca-504b45824fd4" xlink:to="loc_us-gaap_RetirementPlanSponsorLocationAxis_019d8775-5dfe-7e40-892a-eba545123604" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanSponsorLocationDomain_019d8775-5dfe-7e40-892a-eba545123604_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetirementPlanSponsorLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RetirementPlanSponsorLocationAxis_019d8775-5dfe-7e40-892a-eba545123604" xlink:to="loc_us-gaap_RetirementPlanSponsorLocationDomain_019d8775-5dfe-7e40-892a-eba545123604_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanSponsorLocationDomain_019d8775-5dfe-7f57-93c3-6939cb761c1e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetirementPlanSponsorLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RetirementPlanSponsorLocationAxis_019d8775-5dfe-7e40-892a-eba545123604" xlink:to="loc_us-gaap_RetirementPlanSponsorLocationDomain_019d8775-5dfe-7f57-93c3-6939cb761c1e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DomesticPlanMember_019d8775-5dfe-7463-8d63-0fcd841443ba" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DomesticPlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanSponsorLocationDomain_019d8775-5dfe-7f57-93c3-6939cb761c1e" xlink:to="loc_us-gaap_DomesticPlanMember_019d8775-5dfe-7463-8d63-0fcd841443ba" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_US_019d8775-5dfe-78df-8762-d63cfe942e62" xlink:href="https://xbrl.sec.gov/country/2026/country-2026.xsd#country_US"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DomesticPlanMember_019d8775-5dfe-7463-8d63-0fcd841443ba" xlink:to="loc_country_US_019d8775-5dfe-78df-8762-d63cfe942e62" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignPlanMember_019d8775-5dfe-79b1-bd3f-149b21544bc5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ForeignPlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DomesticPlanMember_019d8775-5dfe-7463-8d63-0fcd841443ba" xlink:to="loc_us-gaap_ForeignPlanMember_019d8775-5dfe-79b1-bd3f-149b21544bc5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanServiceCost_019d8775-5dfe-7982-bb43-d49b35cb6999" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DefinedBenefitPlanServiceCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansTableTextBlockLineItems_019d8775-5dfe-75cb-976b-4e8f1cb36fff" xlink:to="loc_us-gaap_DefinedBenefitPlanServiceCost_019d8775-5dfe-7982-bb43-d49b35cb6999" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanInterestCost_019d8775-5dfe-76ab-83cc-9bb69ef2e104" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DefinedBenefitPlanInterestCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansTableTextBlockLineItems_019d8775-5dfe-75cb-976b-4e8f1cb36fff" xlink:to="loc_us-gaap_DefinedBenefitPlanInterestCost_019d8775-5dfe-76ab-83cc-9bb69ef2e104" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets_019d8775-5dfe-750a-9aa5-8dbe96f0d50e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansTableTextBlockLineItems_019d8775-5dfe-75cb-976b-4e8f1cb36fff" xlink:to="loc_us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets_019d8775-5dfe-750a-9aa5-8dbe96f0d50e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses_019d8775-5dfe-7389-9688-1d750e212d6b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansTableTextBlockLineItems_019d8775-5dfe-75cb-976b-4e8f1cb36fff" xlink:to="loc_us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses_019d8775-5dfe-7389-9688-1d750e212d6b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit_019d8775-5dfe-7e76-b8b0-c42138c37476" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansTableTextBlockLineItems_019d8775-5dfe-75cb-976b-4e8f1cb36fff" xlink:to="loc_us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit_019d8775-5dfe-7e76-b8b0-c42138c37476" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost_019d8775-5dfe-7118-9dbe-bd1b55748cd7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansTableTextBlockLineItems_019d8775-5dfe-75cb-976b-4e8f1cb36fff" xlink:to="loc_us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost_019d8775-5dfe-7118-9dbe-bd1b55748cd7" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.unum.com/role/TreasuryStockTransactionsDetails" xlink:type="simple" xlink:href="unm-20260331.xsd#TreasuryStockTransactionsDetails"/>
  <link:definitionLink xlink:role="http://www.unum.com/role/TreasuryStockTransactionsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityClassOfTreasuryStockLineItems_019d8775-5dfe-7b5c-96a0-9f723dbf22c7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityClassOfTreasuryStockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfTreasuryStockTable_019d8775-5dfe-77b4-ba49-9fa81dcaea74" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfTreasuryStockTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EquityClassOfTreasuryStockLineItems_019d8775-5dfe-7b5c-96a0-9f723dbf22c7" xlink:to="loc_us-gaap_ClassOfTreasuryStockTable_019d8775-5dfe-77b4-ba49-9fa81dcaea74" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ShareRepurchaseProgramAxis_019d8775-5dfe-7a8e-a05f-89af2fc45ad3" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ShareRepurchaseProgramAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ClassOfTreasuryStockTable_019d8775-5dfe-77b4-ba49-9fa81dcaea74" xlink:to="loc_srt_ShareRepurchaseProgramAxis_019d8775-5dfe-7a8e-a05f-89af2fc45ad3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ShareRepurchaseProgramDomain_019d8775-5dfe-7a8e-a05f-89af2fc45ad3_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ShareRepurchaseProgramDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ShareRepurchaseProgramAxis_019d8775-5dfe-7a8e-a05f-89af2fc45ad3" xlink:to="loc_srt_ShareRepurchaseProgramDomain_019d8775-5dfe-7a8e-a05f-89af2fc45ad3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ShareRepurchaseProgramDomain_019d8775-5dfe-7c20-a1cc-f8edccba0666" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ShareRepurchaseProgramDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ShareRepurchaseProgramAxis_019d8775-5dfe-7a8e-a05f-89af2fc45ad3" xlink:to="loc_srt_ShareRepurchaseProgramDomain_019d8775-5dfe-7c20-a1cc-f8edccba0666" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_RepurchaseProgramAuthorizedInDecember2025Member_019dc9e3-fa6c-78a5-aee3-f2e707baa1f5" xlink:href="unm-20260331.xsd#unm_RepurchaseProgramAuthorizedInDecember2025Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ShareRepurchaseProgramDomain_019d8775-5dfe-7c20-a1cc-f8edccba0666" xlink:to="loc_unm_RepurchaseProgramAuthorizedInDecember2025Member_019dc9e3-fa6c-78a5-aee3-f2e707baa1f5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_RepurchaseProgramAuthorizedInFebruary2025Member_019d8775-5dfe-7a94-a9c6-29306423053c" xlink:href="unm-20260331.xsd#unm_RepurchaseProgramAuthorizedInFebruary2025Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ShareRepurchaseProgramDomain_019d8775-5dfe-7c20-a1cc-f8edccba0666" xlink:to="loc_unm_RepurchaseProgramAuthorizedInFebruary2025Member_019d8775-5dfe-7a94-a9c6-29306423053c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_RepurchaseProgramAuthorizedInJuly2024Member_019d8775-5dfe-7dc1-8cd8-e3ff932d27b6" xlink:href="unm-20260331.xsd#unm_RepurchaseProgramAuthorizedInJuly2024Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ShareRepurchaseProgramDomain_019d8775-5dfe-7c20-a1cc-f8edccba0666" xlink:to="loc_unm_RepurchaseProgramAuthorizedInJuly2024Member_019d8775-5dfe-7dc1-8cd8-e3ff932d27b6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AcceleratedShareRepurchasesDateAxis_019d8775-5dfe-75a4-839f-a6c9b216752d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AcceleratedShareRepurchasesDateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ClassOfTreasuryStockTable_019d8775-5dfe-77b4-ba49-9fa81dcaea74" xlink:to="loc_us-gaap_AcceleratedShareRepurchasesDateAxis_019d8775-5dfe-75a4-839f-a6c9b216752d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AcceleratedShareRepurchasesDateDomain_019d8775-5dfe-75a4-839f-a6c9b216752d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AcceleratedShareRepurchasesDateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AcceleratedShareRepurchasesDateAxis_019d8775-5dfe-75a4-839f-a6c9b216752d" xlink:to="loc_us-gaap_AcceleratedShareRepurchasesDateDomain_019d8775-5dfe-75a4-839f-a6c9b216752d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AcceleratedShareRepurchasesDateDomain_019d8775-5dfe-7a27-82c7-82b460df73e4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AcceleratedShareRepurchasesDateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AcceleratedShareRepurchasesDateAxis_019d8775-5dfe-75a4-839f-a6c9b216752d" xlink:to="loc_us-gaap_AcceleratedShareRepurchasesDateDomain_019d8775-5dfe-7a27-82c7-82b460df73e4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_November2024AcceleratedShareRepurchaseMember_019d8775-5dfe-70b2-805a-0e8d8b708805" xlink:href="unm-20260331.xsd#unm_November2024AcceleratedShareRepurchaseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcceleratedShareRepurchasesDateDomain_019d8775-5dfe-7a27-82c7-82b460df73e4" xlink:to="loc_unm_November2024AcceleratedShareRepurchaseMember_019d8775-5dfe-70b2-805a-0e8d8b708805" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StockRepurchaseProgramExpirationDate_019d8775-5dfe-7f1f-a08d-64c7a4bc9238" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_StockRepurchaseProgramExpirationDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityClassOfTreasuryStockLineItems_019d8775-5dfe-7b5c-96a0-9f723dbf22c7" xlink:to="loc_srt_StockRepurchaseProgramExpirationDate_019d8775-5dfe-7f1f-a08d-64c7a4bc9238" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StockRepurchaseProgramAuthorizedAmount1_019d8775-5dfe-7c1e-8812-143f174d799b" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_StockRepurchaseProgramAuthorizedAmount1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityClassOfTreasuryStockLineItems_019d8775-5dfe-7b5c-96a0-9f723dbf22c7" xlink:to="loc_srt_StockRepurchaseProgramAuthorizedAmount1_019d8775-5dfe-7c1e-8812-143f174d799b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockValueAcquiredCostMethod_019d8775-5dfe-70cb-8bb9-4485023cda8c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TreasuryStockValueAcquiredCostMethod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityClassOfTreasuryStockLineItems_019d8775-5dfe-7b5c-96a0-9f723dbf22c7" xlink:to="loc_us-gaap_TreasuryStockValueAcquiredCostMethod_019d8775-5dfe-70cb-8bb9-4485023cda8c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchaseProgramRemainingAuthorizedRepurchaseAmount1_019d8775-5dfe-7320-87cc-ba86543b5b4a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockRepurchaseProgramRemainingAuthorizedRepurchaseAmount1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityClassOfTreasuryStockLineItems_019d8775-5dfe-7b5c-96a0-9f723dbf22c7" xlink:to="loc_us-gaap_StockRepurchaseProgramRemainingAuthorizedRepurchaseAmount1_019d8775-5dfe-7320-87cc-ba86543b5b4a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockSharesAcquired_019d8775-5dfe-77f8-b544-e20a539785c2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TreasuryStockSharesAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityClassOfTreasuryStockLineItems_019d8775-5dfe-7b5c-96a0-9f723dbf22c7" xlink:to="loc_us-gaap_TreasuryStockSharesAcquired_019d8775-5dfe-77f8-b544-e20a539785c2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_SharesRepurchasedCostCommissions_019d8775-5dfe-7d8d-aab4-8b21ef7c4864" xlink:href="unm-20260331.xsd#unm_SharesRepurchasedCostCommissions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityClassOfTreasuryStockLineItems_019d8775-5dfe-7b5c-96a0-9f723dbf22c7" xlink:to="loc_unm_SharesRepurchasedCostCommissions_019d8775-5dfe-7d8d-aab4-8b21ef7c4864" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareRepurchaseProgramExciseTax_019dc9eb-2f67-7eff-af9f-f7eb330ebf45" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareRepurchaseProgramExciseTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityClassOfTreasuryStockLineItems_019d8775-5dfe-7b5c-96a0-9f723dbf22c7" xlink:to="loc_us-gaap_ShareRepurchaseProgramExciseTax_019dc9eb-2f67-7eff-af9f-f7eb330ebf45" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AcceleratedShareRepurchasesSettlementPaymentOrReceipt_019d8775-5dfe-7f15-8ce0-9aacf69602e7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AcceleratedShareRepurchasesSettlementPaymentOrReceipt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityClassOfTreasuryStockLineItems_019d8775-5dfe-7b5c-96a0-9f723dbf22c7" xlink:to="loc_us-gaap_AcceleratedShareRepurchasesSettlementPaymentOrReceipt_019d8775-5dfe-7f15-8ce0-9aacf69602e7" xlink:type="arc" order="7"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.unum.com/role/DebtAdditionalInformationDetails" xlink:type="simple" xlink:href="unm-20260331.xsd#DebtAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://www.unum.com/role/DebtAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityLineItems_019d8775-5dfe-7e2d-ae4d-b79356f7ad30" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityTable_019d8775-5dfe-7938-9853-d7d30fa94672" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019d8775-5dfe-7e2d-ae4d-b79356f7ad30" xlink:to="loc_us-gaap_LineOfCreditFacilityTable_019d8775-5dfe-7938-9853-d7d30fa94672" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_019dca08-d906-7016-9c1e-9e19f4ef90c6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_019d8775-5dfe-7938-9853-d7d30fa94672" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_019dca08-d906-7016-9c1e-9e19f4ef90c6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_019dca08-d906-7016-9c1e-9e19f4ef90c6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_019dca08-d906-7016-9c1e-9e19f4ef90c6" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_019dca08-d906-7016-9c1e-9e19f4ef90c6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_019dca09-2fb4-70c3-8109-57292989b27a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_019dca08-d906-7016-9c1e-9e19f4ef90c6" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_019dca09-2fb4-70c3-8109-57292989b27a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_019dca09-5207-724a-88da-96448cfb7a83" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_019dca09-2fb4-70c3-8109-57292989b27a" xlink:to="loc_us-gaap_SubsequentEventMember_019dca09-5207-724a-88da-96448cfb7a83" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_019d8775-5dfe-7e2c-afa9-548582a167ed" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019d8775-5dfe-7e2d-ae4d-b79356f7ad30" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_019d8775-5dfe-7e2c-afa9-548582a167ed" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ExtinguishmentOfDebtAmount_019d8775-5dfe-7c43-86f8-414b64279276" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ExtinguishmentOfDebtAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019d8775-5dfe-7e2d-ae4d-b79356f7ad30" xlink:to="loc_us-gaap_ExtinguishmentOfDebtAmount_019d8775-5dfe-7c43-86f8-414b64279276" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019d8775-5dfe-7064-86ba-ecc79c8bbd27" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019d8775-5dfe-7e2d-ae4d-b79356f7ad30" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019d8775-5dfe-7064-86ba-ecc79c8bbd27" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.unum.com/role/ReinsuranceAdditionalInformationDetail" xlink:type="simple" xlink:href="unm-20260331.xsd#ReinsuranceAdditionalInformationDetail"/>
  <link:definitionLink xlink:role="http://www.unum.com/role/ReinsuranceAdditionalInformationDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectsOfReinsuranceLineItems_019dca3f-75c2-7d09-83f2-754eeda1657f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EffectsOfReinsuranceLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectsOfReinsuranceTable_019dca3a-a4b3-7947-b615-9c472141867c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EffectsOfReinsuranceTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EffectsOfReinsuranceLineItems_019dca3f-75c2-7d09-83f2-754eeda1657f" xlink:to="loc_us-gaap_EffectsOfReinsuranceTable_019dca3a-a4b3-7947-b615-9c472141867c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_SignificantTransactionAxis_019dca3b-3572-7a39-a975-29acdbb8bf81" xlink:href="unm-20260331.xsd#unm_SignificantTransactionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_EffectsOfReinsuranceTable_019dca3a-a4b3-7947-b615-9c472141867c" xlink:to="loc_unm_SignificantTransactionAxis_019dca3b-3572-7a39-a975-29acdbb8bf81" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_SignificantTransactionDomain_019dca3b-3572-7a39-a975-29acdbb8bf81_default" xlink:href="unm-20260331.xsd#unm_SignificantTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_unm_SignificantTransactionAxis_019dca3b-3572-7a39-a975-29acdbb8bf81" xlink:to="loc_unm_SignificantTransactionDomain_019dca3b-3572-7a39-a975-29acdbb8bf81_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_SignificantTransactionDomain_019dca3b-6f2f-7202-83ac-79cf36e467a0" xlink:href="unm-20260331.xsd#unm_SignificantTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_unm_SignificantTransactionAxis_019dca3b-3572-7a39-a975-29acdbb8bf81" xlink:to="loc_unm_SignificantTransactionDomain_019dca3b-6f2f-7202-83ac-79cf36e467a0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_LongTermCareAndIndividualDisabilityReinsuranceTransactionMember_019dca3b-9cb2-78a0-a3b5-c2142fcef11d" xlink:href="unm-20260331.xsd#unm_LongTermCareAndIndividualDisabilityReinsuranceTransactionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_unm_SignificantTransactionDomain_019dca3b-6f2f-7202-83ac-79cf36e467a0" xlink:to="loc_unm_LongTermCareAndIndividualDisabilityReinsuranceTransactionMember_019dca3b-9cb2-78a0-a3b5-c2142fcef11d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_019dca3c-1fcc-742a-a9df-5600422bac22" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_EffectsOfReinsuranceTable_019dca3a-a4b3-7947-b615-9c472141867c" xlink:to="loc_srt_ProductOrServiceAxis_019dca3c-1fcc-742a-a9df-5600422bac22" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019dca3c-1fcc-742a-a9df-5600422bac22_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_019dca3c-1fcc-742a-a9df-5600422bac22" xlink:to="loc_srt_ProductsAndServicesDomain_019dca3c-1fcc-742a-a9df-5600422bac22_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019dca3c-3626-7e3a-b7bb-11e2640ab67c" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_019dca3c-1fcc-742a-a9df-5600422bac22" xlink:to="loc_srt_ProductsAndServicesDomain_019dca3c-3626-7e3a-b7bb-11e2640ab67c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_LongTermCareMember_019dca3c-b4ca-7933-92f5-d881636f9334" xlink:href="unm-20260331.xsd#unm_LongTermCareMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019dca3c-3626-7e3a-b7bb-11e2640ab67c" xlink:to="loc_unm_LongTermCareMember_019dca3c-b4ca-7933-92f5-d881636f9334" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_IndividualDisabilityMember_019dca3c-d4d7-7cd3-bb8f-75d228beb6f5" xlink:href="unm-20260331.xsd#unm_IndividualDisabilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019dca3c-3626-7e3a-b7bb-11e2640ab67c" xlink:to="loc_unm_IndividualDisabilityMember_019dca3c-d4d7-7cd3-bb8f-75d228beb6f5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019dca3d-bd92-7316-bc18-b316d59fb306" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_EffectsOfReinsuranceTable_019dca3a-a4b3-7947-b615-9c472141867c" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019dca3d-bd92-7316-bc18-b316d59fb306" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019dca3d-bd92-7316-bc18-b316d59fb306_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019dca3d-bd92-7316-bc18-b316d59fb306" xlink:to="loc_us-gaap_SegmentDomain_019dca3d-bd92-7316-bc18-b316d59fb306_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019dca3d-e058-7a4d-bbab-99baee20a891" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019dca3d-bd92-7316-bc18-b316d59fb306" xlink:to="loc_us-gaap_SegmentDomain_019dca3d-e058-7a4d-bbab-99baee20a891" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_UnumUsMember_019dca3e-0d99-7e64-b213-250bb353043c" xlink:href="unm-20260331.xsd#unm_UnumUsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019dca3d-e058-7a4d-bbab-99baee20a891" xlink:to="loc_unm_UnumUsMember_019dca3e-0d99-7e64-b213-250bb353043c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_ClosedBlockMember_019dca3e-2a56-7cd6-b889-21f62efde8a8" xlink:href="unm-20260331.xsd#unm_ClosedBlockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019dca3d-e058-7a4d-bbab-99baee20a891" xlink:to="loc_unm_ClosedBlockMember_019dca3e-2a56-7cd6-b889-21f62efde8a8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_019dca3e-8663-7a67-8c95-565bb71508ee" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_EffectsOfReinsuranceTable_019dca3a-a4b3-7947-b615-9c472141867c" xlink:to="loc_srt_ConsolidationItemsAxis_019dca3e-8663-7a67-8c95-565bb71508ee" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019dca3e-8663-7a67-8c95-565bb71508ee_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_019dca3e-8663-7a67-8c95-565bb71508ee" xlink:to="loc_srt_ConsolidationItemsDomain_019dca3e-8663-7a67-8c95-565bb71508ee_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019dca3e-9d9e-746b-8709-6ba2d5e47ace" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_019dca3e-8663-7a67-8c95-565bb71508ee" xlink:to="loc_srt_ConsolidationItemsDomain_019dca3e-9d9e-746b-8709-6ba2d5e47ace" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_019dca3e-d981-780d-9307-b731dbc121dd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_019dca3e-9d9e-746b-8709-6ba2d5e47ace" xlink:to="loc_us-gaap_OperatingSegmentsMember_019dca3e-d981-780d-9307-b731dbc121dd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_NetCashPaidInRelationToReinsuranceAgreement_019dca3f-c7c8-7616-a1c7-8fb31d36b123" xlink:href="unm-20260331.xsd#unm_NetCashPaidInRelationToReinsuranceAgreement"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectsOfReinsuranceLineItems_019dca3f-75c2-7d09-83f2-754eeda1657f" xlink:to="loc_unm_NetCashPaidInRelationToReinsuranceAgreement_019dca3f-c7c8-7616-a1c7-8fb31d36b123" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_019dca40-7db5-7b7f-b7da-73e42b0c086c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectsOfReinsuranceLineItems_019dca3f-75c2-7d09-83f2-754eeda1657f" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_019dca40-7db5-7b7f-b7da-73e42b0c086c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedInvestmentIncomeReceivable_019dca40-d24b-705e-a4c9-0a3d17bd7dc2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccruedInvestmentIncomeReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectsOfReinsuranceLineItems_019dca3f-75c2-7d09-83f2-754eeda1657f" xlink:to="loc_us-gaap_AccruedInvestmentIncomeReceivable_019dca40-d24b-705e-a4c9-0a3d17bd7dc2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_NegativeCedingCommission_019dca40-f696-7adb-b02f-5755ed508b70" xlink:href="unm-20260331.xsd#unm_NegativeCedingCommission"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectsOfReinsuranceLineItems_019dca3f-75c2-7d09-83f2-754eeda1657f" xlink:to="loc_unm_NegativeCedingCommission_019dca40-f696-7adb-b02f-5755ed508b70" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnInvestments_019dca41-36a4-78dd-97f5-d3cae59a2727" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainLossOnInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectsOfReinsuranceLineItems_019dca3f-75c2-7d09-83f2-754eeda1657f" xlink:to="loc_us-gaap_GainLossOnInvestments_019dca41-36a4-78dd-97f5-d3cae59a2727" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReinsuranceRecoverables_019dca41-79f0-7101-a32c-e330b2d1e055" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReinsuranceRecoverables"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectsOfReinsuranceLineItems_019dca3f-75c2-7d09-83f2-754eeda1657f" xlink:to="loc_us-gaap_ReinsuranceRecoverables_019dca41-79f0-7101-a32c-e330b2d1e055" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_DeferredLossOnReinsurance_019dca42-427e-7e95-9918-394adbb5bdb4" xlink:href="unm-20260331.xsd#unm_DeferredLossOnReinsurance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectsOfReinsuranceLineItems_019dca3f-75c2-7d09-83f2-754eeda1657f" xlink:to="loc_unm_DeferredLossOnReinsurance_019dca42-427e-7e95-9918-394adbb5bdb4" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_unm_DeferredGainOnReinsurance_019dca42-5dea-729e-a9bf-02a4da193087" xlink:href="unm-20260331.xsd#unm_DeferredGainOnReinsurance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectsOfReinsuranceLineItems_019dca3f-75c2-7d09-83f2-754eeda1657f" xlink:to="loc_unm_DeferredGainOnReinsurance_019dca42-5dea-729e-a9bf-02a4da193087" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredPolicyAcquisitionCostsPeriodIncreaseDecrease_019dca42-954c-770f-8245-cadb90b0b953" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredPolicyAcquisitionCostsPeriodIncreaseDecrease"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectsOfReinsuranceLineItems_019dca3f-75c2-7d09-83f2-754eeda1657f" xlink:to="loc_us-gaap_DeferredPolicyAcquisitionCostsPeriodIncreaseDecrease_019dca42-954c-770f-8245-cadb90b0b953" xlink:type="arc" order="8"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fasb.org/srt/role/srt-eedm/ExtensibleEnumerationLists" xlink:type="simple" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-roles-2026.xsd#eedm1"/>
  <link:definitionLink xlink:role="http://fasb.org/srt/role/srt-eedm/ExtensibleEnumerationLists" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsAbstract"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLongTermInvestments" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherLongTermInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract" xlink:to="loc_us-gaap_OtherLongTermInvestments" xlink:type="arc" order="101"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities" xlink:type="arc" order="102"/>
  </link:definitionLink>
</link:linkbase>
