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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2020-12-28</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000813762</issuerCik>
        <issuerName>ICAHN ENTERPRISES L.P.</issuerName>
        <issuerTradingSymbol>IEP</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001312913</rptOwnerCik>
            <rptOwnerName>Krongard A B</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O ICAHN ENTERPRISES L.P.</rptOwnerStreet1>
            <rptOwnerStreet2>16690 COLLINS AVENUE - PH-1</rptOwnerStreet2>
            <rptOwnerCity>SUNNY ISLES BEACH</rptOwnerCity>
            <rptOwnerState>FL</rptOwnerState>
            <rptOwnerZipCode>33160</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Depositary Units</value>
                <footnoteId id="F1"/>
            </securityTitle>
            <transactionDate>
                <value>2020-12-28</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>19285</value>
                    <footnoteId id="F2"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>51.0052</value>
                    <footnoteId id="F3"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>36008</value>
                    <footnoteId id="F4"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>Please see footnotes</value>
                    <footnoteId id="F2"/>
                    <footnoteId id="F4"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">Depository Units representing limited partner interests (&quot;Depository Units&quot;) in Icahn Enterprises L.P. (the &quot;Issuer&quot;).</footnote>
        <footnote id="F2">Represents Depository Units purchased by The Krongard Foundation Inc. Mr. Krongard may be deemed to indirectly beneficially own these Depository Units. Mr. Krongard disclaims beneficial ownership of such Depositary Units except to the extent of his pecuniary interest therein.</footnote>
        <footnote id="F3">Represents the weighted average purchase price of multiple transactions, with Depository Units purchased at prices ranging from $50.82 to $51.24 per Depository Unit. The reporting person hereby undertakes to provide, upon request by the U.S. Securities and Exchange Commission staff, the Issuer or a unitholder of the Issuer, full information regarding the number of Depository Units purchased at each separate price.</footnote>
        <footnote id="F4">Includes 16,723 Depository Units owned by Mr. Krongard's spouse. Mr. Krongard may be deemed to indirectly beneficially own these Depository Units. Mr. Krongard disclaims beneficial ownership of such Depositary Units for all purposes.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/S/ Alvin B. Krongard</signatureName>
        <signatureDate>2020-12-30</signatureDate>
    </ownerSignature>
</ownershipDocument>
