Exhibit 24

                                POWER OF ATTORNEY

         Know all by these presents, that the undersigned hereby constitutes and
appoints each of Emma Cuadrado and John R. Flynn, signing singly, the
undersigned's true and lawful attorney-in-fact to:

         (1) execute for and on behalf of the undersigned, all reports to be
         filed by the undersigned pursuant to Section 16(a) of the Securities
         Exchange Act of 1934, as amended (the "Exchange Act") and the rules
         promulgated thereunder (including Forms 3, 4, and 5 and any successor
         forms) (the "Section 16 Reports") with respect to the equity securities
         of KCG Holdings, Inc. (the "Company");

         (2) do and perform any and all acts for and on behalf of the
         undersigned that may be necessary or desirable to complete and execute
         any such Section 16 Report, complete and execute any amendment or
         amendments thereto, and file such report with the United States
         Securities and Exchange Commission and any stock exchange or similar
         authority; and

         (3) take any other action of any type whatsoever in connection with the
         foregoing that, in the opinion of such attorney-in-fact, may be of
         benefit to, in the best interest of, or legally required by, the
         undersigned, it being understood that the documents executed by such
         attorney-in-fact on behalf of the undersigned pursuant to this Power of
         Attorney shall be in such form and shall contain such terms and
         conditions as such attorney-in-fact may approve in such
         attorney-in-fact's discretion.

         The powers granted above may be exercised by each such attorney-in-fact
on behalf of the undersigned, individually. The undersigned hereby grants to
each such attorney-in-fact full power and authority to do and perform any and
every act and thing whatsoever requisite, necessary, or proper to be done in the
exercise of any of the rights and powers herein granted, as fully to all intents
and purposes as the undersigned might or could do if personally present, with
full power of substitution or revocation, hereby ratifying and confirming all
that such attorney-in-fact, or such attorney-in-fact's substitute or
substitutes, shall lawfully do or cause to be done by virtue of this Power of
Attorney and the rights and powers herein granted. The undersigned acknowledges
that the foregoing attorneys-in-fact, in serving in such capacity at the request
of the undersigned, are not assuming any of the undersigned's responsibilities
to comply with Section 16 of the Exchange Act.

         This Power of Attorney shall be effective as of the date set forth
below and shall continue in full force and effect until the undersigned is no
longer required to file Section 16 Reports with respect to the equity securities
of the Company, unless earlier revoked by the undersigned in a signed writing
delivered to the foregoing attorneys-in-fact.

         IN WITNESS WHEREOF, the undersigned has caused this Power of Attorney
to be executed as of this 27th day of June, 2013.

The Daniel V. Tierney 2011 Trust
By: Emma Cuadrado and John R. Flynn, as Co-trustees

Signature: /s/ Emma Cuadrado
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Name:  Emma Cuadrado

Signature: /s/ John  R. Flynn
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Name:  John R. Flynn