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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2013-03-20</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001351541</issuerCik>
        <issuerName>Delek US Holdings, Inc.</issuerName>
        <issuerTradingSymbol>DK</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001361020</rptOwnerCik>
            <rptOwnerName>Delek Hungary Holding LTD Liability CO</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>7, GIBOREI ISRAEL STREET, P.O.B. 8464</rptOwnerStreet1>
            <rptOwnerStreet2>INDUSTRIAL ZONE SOUTH</rptOwnerStreet2>
            <rptOwnerCity>NETANYA</rptOwnerCity>
            <rptOwnerState>L3</rptOwnerState>
            <rptOwnerZipCode>42504</rptOwnerZipCode>
            <rptOwnerStateDescription>ISRAEL</rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2013-03-20</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>9000000</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>37.92</value>
                    <footnoteId id="F2"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>22536432</value>
                    <footnoteId id="F3"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                    <footnoteId id="F3"/>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2013-03-20</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>1000000</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>37.92</value>
                    <footnoteId id="F2"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>21536432</value>
                    <footnoteId id="F3"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                    <footnoteId id="F3"/>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">This Form 4 is filed jointly by Delek Hungary Holding Limited Liability Company (&quot;Delek Hungary&quot;), Delek Petroleum, Ltd. (&quot;Delek Petroleum&quot;), Delek Group, Ltd. (&quot;Delek Group&quot;) and Itshak Sharon.  On March 20, 2013, Delek Hungary sold 9,000,000 shares of Common Stock of Delek US Holdings, Inc. (&quot;Delek US&quot;) in an underwritten secondary offering (the &quot;Offering&quot;).  Concurrently with and contingent on the closing of the Offering, Delek US repurchased 1,000,000 shares of its common stock from Delek Hungary in a private, non-underwritten transaction (the &quot;Repurchase&quot;).  Delek Petroleum, Delek Group and Mr. Sharon disclaim beneficial ownership of these shares except to the extent of their pecuniary interest therein.</footnote>
        <footnote id="F2">The price represents the public offering price of $39.50 per share less the underwriters' discount of $1.58 per share.  The price per share in connection with the Repurchase was equal to the price per share paid by the underwriters in connection with the Offering.</footnote>
        <footnote id="F3">Represents shares directly owned by Delek Hungary.  Delek Hungary is a subsidiary of Delek Petroleum and Delek Group.  Mr. Sharon has voting and investment control over Delek Group, the parent company of Delek Petroleum and Delek Hungary, through corporations that he controls.  Delek Petroleum, Delek Group and Mr. Sharon disclaim beneficial ownership of these shares except to the extent of their pecuniary interest therein.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Leora Pratt Levin, Attorney-In-Fact</signatureName>
        <signatureDate>2013-03-22</signatureDate>
    </ownerSignature>
</ownershipDocument>
