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

    <schemaVersion>X0206</schemaVersion>

    <documentType>3</documentType>

    <periodOfReport>2013-03-12</periodOfReport>

    <noSecuritiesOwned>0</noSecuritiesOwned>

    <issuer>
        <issuerCik>0001508655</issuerCik>
        <issuerName>TPG Specialty Lending, Inc.</issuerName>
        <issuerTradingSymbol>NA</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001574849</rptOwnerCik>
            <rptOwnerName>Mello Jennifer</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O TPG GLOBAL, LLC</rptOwnerStreet1>
            <rptOwnerStreet2>301 COMMERCE STREET, SUITE 3300</rptOwnerStreet2>
            <rptOwnerCity>FORT WORTH</rptOwnerCity>
            <rptOwnerState>TX</rptOwnerState>
            <rptOwnerZipCode>76102</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Vice President</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeHolding>
            <securityTitle>
                <value>No securities beneficially owned</value>
                <footnoteId id="F1"/>
                <footnoteId id="F2"/>
                <footnoteId id="F3"/>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">Jennifer Mello does not directly own any securities of TPG Specialty Lending, Inc. (the &quot;Issuer&quot;).</footnote>
        <footnote id="F2">Ms. Mello is a Vice President of the Issuer and General Counsel to TPG Special Situations Partners, L.P., which is affiliated with TPG Group Holdings (SBS) Advisors, Inc., a Delaware corporation (&quot;Group Advisors&quot;), and Tarrant Capital Advisors, Inc. a Delaware corporation (&quot;Tarrant Capital&quot;).  As of the date hereof, Group Advisors may be deemed to beneficially own 33,177 shares of Common Stock (the &quot;TSL Stock&quot;) of the Issuer. As of the date hereof, Tarrant Capital may be deemed to beneficially own (i) 28,146 shares of the TSL Stock, (ii) 5,544 shares of Common Stock held by TSL FOF, L.P., a Delaware limited partnership, and (iii) 1 share of Common Stock held by Tarrant Advisors, Inc., a Texas corporation.</footnote>
        <footnote id="F3">Ms. Mello disclaims beneficial ownership of the shares of Common Stock that are or may be beneficially owned by Group Holdings or Tarrant Capital or any of their respective  affiliates.  Pursuant to Rule 16a-1(a)(4) under the Securities Exchange Act of 1934, as amended (the &quot;Exchange Act&quot;), this filing shall not be deemed an admission that Ms. Mello is, for purposes of Section 16 of the Exchange Act or otherwise, the beneficial owner of any securities of the Issuer directly held by Group Advisors, Tarrant Capital or any of their affiliates.</footnote>
    </footnotes>

    <remarks>4. Ronald Cami is signing on behalf of Jennifer Mello pursuant to the authorization and designation letter dated April 15, 2013, which is attached here as an exhibit.</remarks>

    <ownerSignature>
        <signatureName>By: Ronald Cami on behalf of Jennifer Mello (4)</signatureName>
        <signatureDate>2013-04-19</signatureDate>
    </ownerSignature>
</ownershipDocument>
