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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2013-02-13</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001273801</issuerCik>
        <issuerName>NORTHSTAR REALTY FINANCE CORP.</issuerName>
        <issuerTradingSymbol>NRF</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001541849</rptOwnerCik>
            <rptOwnerName>Lieberman Ronald J.</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>399 PARK AVENUE, 18TH FLOOR</rptOwnerStreet1>
            <rptOwnerStreet2>C/O NORTHSTAR REALTY FINANCE CORP.</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10022</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>EVP, GC and Secretary</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable></nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Performance Restricted Stock Units</value>
                <footnoteId id="F1"/>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F1"/>
                <footnoteId id="F2"/>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2013-02-13</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>40860</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F1"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F1"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>40860</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>40860</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
        <derivativeTransaction>
            <securityTitle>
                <value>LTIP Units</value>
                <footnoteId id="F3"/>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F2"/>
                <footnoteId id="F3"/>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2013-02-13</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>40860</value>
                    <footnoteId id="F4"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F4"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F3"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>40860</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>40860</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">These performance restricted stock units (&quot;RSUs&quot;) were granted as long-term performance based incentive compensation for 2012 pursuant to NorthStar Realty Finance Corp.'s (the &quot;Company&quot;) Executive Incentive Bonus Plan for 2012. The RSUs will vest in full as of December 31, 2015 if the total stockholder return from January 1, 2012 through December 31, 2015 equals or exceeds 12% per year, compounded annually, and vest in part if the annual total stockholder return during this period is equal to 6% per year, compounded annually, or greater. If earned each RSU will be settled, in shares of common stock, par value $0.01 per share of the Company (&quot;Common Stock&quot;) or LTIP Units, if available, otherwise in cash. These RSUs will expire and cease to exist following settlement.</footnote>
        <footnote id="F2">The aggregate cash amount payable pursuant to these LTIP Units and RSUs, to the extent earned and to the extent shares of Common Stock, or LTIP Units, as the case may be with respect to the RSUs, are not available to be issued upon their redemption or settlement, respectively, may not exceed two times the initial dollar value of the reporting person's long-term bonus for 2012 under the Company's Executive Incentive Bonus Plan, which was used to determine the number of LTIP Units and RSUs to be awarded.</footnote>
        <footnote id="F3">Represents units of limited partnership interest structured as profits interests in NorthStar Realty Finance Limited Partnership (&quot;NRFLP&quot;), a majority-owned subsidiary and the operating partnership of the Company. Conditioned on minimum allocations to the capital accounts of the LTIP Unit for federal income tax purposes, each LTIP Unit may be converted, at the election of the holder, into one common unit of limited partnership interest in NRFLP. Each of the OP Units underlying these LTIP Units are redeemable at the election of the OP Unit holder for (1) cash equal to the then fair market value of one (1) share of Common Stock or (2) at the option of the Company in its capacity as general partner of NRFLP, one (1) share of Common Stock. The rights to convert LTIP Units into OP Units and redeem OP Units do not have expiration dates.</footnote>
        <footnote id="F4">These LTIP Units were granted as long-term incentive compensation for 2012 pursuant to the Company's Executive Incentive Bonus Plan for 2012. These LTIP Units vest as to 25% of the LTIP Units on each of the grant date, and January 29, 2014, 2015 and 2016, respectively. Notwithstanding the foregoing, none of these LTIP Units may be redeemed prior to December 31, 2015.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Ronald J. Lieberman</signatureName>
        <signatureDate>2013-02-15</signatureDate>
    </ownerSignature>
</ownershipDocument>
