<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0206</schemaVersion>

    <documentType>3</documentType>

    <periodOfReport>2015-06-24</periodOfReport>

    <noSecuritiesOwned>0</noSecuritiesOwned>

    <issuer>
        <issuerCik>0001552033</issuerCik>
        <issuerName>TransUnion</issuerName>
        <issuerTradingSymbol>TRU</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001645871</rptOwnerCik>
            <rptOwnerName>Klemann Gilbert H</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O GOLDMAN, SACHS &amp; CO.</rptOwnerStreet1>
            <rptOwnerStreet2>200 WEST STREET</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10282</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock, $0.01 par value</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>72355340</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See footnotes</value>
                    <footnoteId id="F1"/>
                    <footnoteId id="F2"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">The Reporting Person is a managing director of Goldman, Sachs &amp; Co. (&quot;Goldman Sachs&quot;). Goldman Sachs is a wholly-owned subsidiary of The Goldman Sachs Group, Inc. (&quot;GS Group&quot;). The Reporting Person disclaims beneficial ownership of the securities reported herein except to the extent of his pecuniary interest therein, if any, and this report shall not be deemed an admission that any such person or entity is the beneficial owner of, or has any pecuniary interest in, such securities for purposes of Section 16 of the Securities Exchange Act of 1934, as amended, or for any other purpose.</footnote>
        <footnote id="F2">Goldman Sachs and GS Group may be deemed to beneficially own indirectly, in the aggregate, 72,355,340 shares of common stock, par value $0.01 per share, of Transunion by reason of the direct beneficial ownership of such shares by certain investment partnerships (the &quot;Funds&quot;) because affiliates of Goldman Sachs and GS Group are the general partner, managing general partner, managing partner, managing member or member of the Funds. Goldman Sachs is the investment manager of certain of the Funds.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Yvette Kosic, Attorney-in-fact</signatureName>
        <signatureDate>2015-06-29</signatureDate>
    </ownerSignature>
</ownershipDocument>
