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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2014-08-11</periodOfReport>

    <notSubjectToSection16>1</notSubjectToSection16>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001527270</rptOwnerCik>
            <rptOwnerName>MSSB TPG Specialty Lending Onshore Feeder Fund</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O MORGAN STANLEY GWM FEEDER STRATEGIES</rptOwnerStreet1>
            <rptOwnerStreet2>LLC, 522 FIFTH AVENUE, 13TH FLOOR</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10036</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2014-08-11</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>2593099</value>
                    <footnoteId id="F1"/>
                    <footnoteId id="F2"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>18.07</value>
                    <footnoteId id="F3"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>3012582</value>
                    <footnoteId id="F2"/>
                    <footnoteId id="F4"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>31948</value>
                    <footnoteId id="F5"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>Owned by an affiliate</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Morgan Stanley GWM Feeder Strategies LLC is the managing owner of the Reporting Person, and is a wholly-owned subsidiary of Morgan Stanley Smith Barney Holdings LLC. Morgan Stanley Smith Barney Holdings LLC is indirectly majority-owned by Morgan Stanley.</footnote>
        <footnote id="F2">The Reporting Person disclaims beneficial ownership of these securities except to the extent of its pecuniary interest therein, and this Form 4 shall not be deemed an admission that the Reporting Person is the beneficial owner of the securities for purposes of Section 16 or for any other purpose.</footnote>
        <footnote id="F3">The Reporting Person, along with the other selling stockholders and the Issuer, has entered into an Underwriting Agreement with Merrill Lynch, Pierce, Fenner &amp; Smith Incorporated, J.P. Morgan Securities LLC and Goldman, Sachs &amp; Co., as representatives of the several underwriters, for the sale of the shares of Common Stock at a price per share of $18.0711.</footnote>
        <footnote id="F4">Although MSSB TPG Specialty Lending Onshore Feeder Fund (the &quot;Trust&quot;) beneficially owns 3,012,582 shares of the common stock of the Issuer and would otherwise be entitled to vote such shares, the Trust has contractually agreed to pass such voting rights through to the Trust's underlying investors (each a &quot;Unitholder&quot; and collectively, the &quot;Unitholders&quot;) pro rata in accordance with each Unitholder's relative ownership of units of the Trust. Each Unitholder will make its own determination as to how to vote with respect to its portion of the Trust's shares of the Issuer, as well as whether or not to vote with respect to such shares.  If Unitholders representing a certain percentage vote their interests, the Trust will vote all shares in accordance with the votes received. If, however, less than the agreed upon representative vote is received, the Trust will not vote any of the shares.</footnote>
        <footnote id="F5">On March 21, 2014, Morgan Stanley Capital Services LLC (&quot;MSCS&quot;) acquired 31,948 shares of the Issuer at a price of $16.0774 per share.  MSCS is indirectly wholly-owned by Morgan Stanley.  Notwithstanding the filing of this Form 4, the Reporting Person disclaims beneficial ownership of the 31,948 shares of common stock acquired by MSCS.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Michael Korn, on behalf of Morgan Stanley GWM Feeder Strategies LLC, the managing owner of the reporting person</signatureName>
        <signatureDate>2014-08-13</signatureDate>
    </ownerSignature>
</ownershipDocument>
