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

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2009-12-14</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001361468</rptOwnerCik>
            <rptOwnerName>Sharon Itshak</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>2009-12-14</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>22971</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>5.8395</value>
                    <footnoteId id="F1"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>39636432</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See footnote</value>
                    <footnoteId id="F2"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2009-12-15</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>100000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>5.8969</value>
                    <footnoteId id="F3"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>39736432</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See footnote</value>
                    <footnoteId id="F4"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">The purchase price is a weighted average resulting from four different purchase prices ranging between $5.8171 and $5.95.  The reporting person will maintain documentation that shows the number of shares purchased at each separate price, and, upon written request, will provide this information to the SEC staff, the issuer, or a security holder of the issuer.</footnote>
        <footnote id="F2">Represents 39,389,869 and 246,563 shares owned of record by Delek Hungary Holding Limited Liability Company and Delek Petroleum, Ltd. respectively.  Mr. Sharon disclaims beneficial ownership of these shares except to the extent of its pecuniary interest therein.</footnote>
        <footnote id="F3">The purchase price is a weighted average resulting from 12 different purchase prices ranging between $5.8373 and $5.9947.  The reporting person will maintain documentation that shows the number of shares purchased at each separate price, and, upon written request, will provide this information to the SEC staff, the issuer, or a security holder of the issuer.</footnote>
        <footnote id="F4">Represents 39,389,869 and 346,563 shares owned of record by Delek Hungary Holding Limited Liability Company and Delek Petroleum, Ltd. respectively.  Mr. Sharon disclaims beneficial ownership of these shares except to the extent of its pecuniary interest therein.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Leora Pratt Levin, Attorney-In-Fact</signatureName>
        <signatureDate>2009-12-16</signatureDate>
    </ownerSignature>
</ownershipDocument>
