Exhibit 3.1

CERTIFICATE OF DESIGNATIONS

OF

SERIES A PARTICIPATING CUMULATIVE PREFERRED STOCK

OF

GAIN CAPITAL HOLDINGS, INC.

GAIN Capital Holdings, Inc., a corporation organized and existing under the laws of the State of Delaware (the “Corporation”), in accordance with the provisions of Section 151 of the General Corporation Law of the State of Delaware thereof, does hereby certify:

The board of directors of the Corporation (the “Board of Directors”) or a duly authorized committee of the Board of Directors, in accordance with the certificate of incorporation and bylaws of the Corporation and applicable law, adopted the following resolution on April 9, 2013 creating a series of preferred stock of the Corporation from its blank check preferred stock authority designated as “Series A Preferred Stock”.

RESOLVED, that pursuant to the provisions of the certificate of incorporation and the bylaws of the Corporation and applicable law, a series of preferred stock, created from its blank check preferred stock authority, par value $0.00001 per share, of the Corporation be and hereby is created, and that the designation and number of shares of such series, and the voting and other powers, preferences and relative, participating, optional or other rights, and the qualifications, limitations and restrictions thereof, of the shares of such series, are as follows:

Section 1. Designation and Number of Shares. The shares of such series shall be designated as “Series A Participating Cumulative Preferred Stock” (the “Series A Preferred Stock”), and the number of shares constituting such series shall be 600,000. Such number of shares of the Series A Preferred Stock may be increased or decreased by resolution of the Board of Directors; provided that no decrease shall reduce the number of shares of Series A Preferred Stock to a number less than the number of shares then outstanding plus the number of shares issuable upon exercise or conversion of outstanding rights, options or other securities issued by the Corporation.

Section 2. Dividends and Distributions. (a) Subject to the rights of the holders of any shares of any class or series of stock of the Corporation ranking prior and superior to the shares of Series A Preferred Stock with respect to dividends, the holders of shares of Series A Preferred Stock, in preference to the holders of Common Stock, par value $0.00001 per share (the “Common Stock”) and any other shares of any class or series of stock of the Corporation ranking junior to the Series A Preferred Stock in respect thereof, shall be entitled to receive, when, as and if declared by the Board of Directors out of funds legally available for the purpose, quarterly dividends payable on the last day of March, June, September and December of each year (each such date being referred to

herein as a “Quarterly Dividend Payment Date”), commencing on the first Quarterly Dividend Payment Date after the first issuance of any share or fraction of a share of Series A Preferred Stock, in an amount per share (rounded to the nearest cent) equal to the greater of (i) $1.00 and (ii) the Multiplier Number (as hereinafter defined) then in effect times the aggregate per share amount of all cash dividends or other distributions and the then Multiplier Number then in effect times the aggregate per share amount (payable in kind) of all non-cash dividends or other distributions (other than (A) a dividend payable in shares of Common Stock, or (B) a subdivision of the outstanding shares of Common Stock (by reclassification or otherwise)), declared on the Common Stock since the immediately preceding Quarterly Dividend Payment Date, or, with respect to the first Quarterly Dividend Payment Date, since the first issuance of any share or fraction of a share of Series A Preferred Stock. As used herein, the “Multiplier Number” shall be 100; provided that if, at any time after April 9, 2013 (the “Rights Declaration Date”), the Company shall (i) declare or pay any dividend on the Common Stock payable in shares of Common Stock or make any distribution on the Common Stock in shares of Common Stock, (ii) subdivide (by a stock split or otherwise) the outstanding shares of Common Stock into a larger number of shares of Common Stock or (iii) combine (by a reverse stock split or otherwise) the outstanding shares of Common Stock into a smaller number of shares of Common Stock, then in each such event the Multiplier Number shall be adjusted to a number determined by multiplying the Multiplier Number in effect immediately prior to such event by a fraction, the numerator of which is the number of shares of Common Stock that are outstanding immediately after such event and the denominator of which is the number of shares of Common Stock that are outstanding immediately prior to such event (and rounding the result to the nearest whole number); and provided further that, if at any time after the Rights Declaration Date, the Company shall issue any shares of its capital stock in a merger, reclassification, or change of the outstanding shares of Common Stock, then in each such event the Multiplier Number shall be appropriately adjusted to reflect such merger, reclassification or change so that each share of Preferred Stock continues to be the economic equivalent of a Multiplier Number of shares of Common Stock prior to such merger, reclassification or change.

(b) The Corporation shall declare a dividend or distribution on the Series A Preferred Stock as provided in Section 2(a) at the same time it declares a dividend or distribution on the Common Stock (other than a dividend payable in shares of Common Stock); provided that if no dividend or distribution shall have been declared on the Common Stock during the period between any Quarterly Dividend Payment Date and the next subsequent Quarterly Dividend Payment Date (or, with respect to the first Quarterly Dividend Payment Date, the period between the first issuance of any share or fraction of a share of Series A Preferred Stock and such first Quarterly Dividend Payment Date), a dividend of $1.00 per share on the Series A Preferred Stock shall nevertheless be payable on such subsequent Quarterly Dividend Payment Date.

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(c) Dividends shall begin to accrue and be cumulative on outstanding shares of Series A Preferred Stock from the Quarterly Dividend Payment Date next preceding the date of issuance of such shares of Series A Preferred Stock, unless the date of issuance of such shares is on or before the record date for the first Quarterly Dividend Payment Date, in which case dividends on such shares shall begin to accrue and be cumulative from the date of issue of such shares, or unless the date of issue is a date after the record date for the determination of holders of shares of Series A Preferred Stock entitled to receive a quarterly dividend and on or before such Quarterly Dividend Payment Date, in which case dividends shall begin to accrue and be cumulative from such Quarterly Dividend Payment Date. Accrued but unpaid dividends shall not bear interest. Dividends paid on shares of Series A Preferred Stock in an amount less than the total amount of such dividends at the time accrued and payable on such shares shall be allocated pro rata on a share-by-share basis among all such shares at the time outstanding. The Board of Directors may fix a record date for the determination of holders of shares of Series A Preferred Stock entitled to receive payment of a dividend or distribution declared thereon, which record date shall not be more than 60 days prior to the date fixed for the payment thereof.

(d) So long as any shares of Series A Preferred Stock are outstanding, no dividends or other distributions shall be declared, paid or distributed, or set aside for payment or distribution on the Common Stock unless, in each case, the dividend required by this Section 2 to be declared on the Series A Preferred Stock shall have been declared and set aside.

(e) The holders of shares of Series A Preferred Stock shall not be entitled to receive any dividends or other distributions except as herein provided.

Section 3. Voting Rights. In addition to any other voting rights required by law, the holders of shares of Series A Preferred Stock shall have the following voting rights:

(a) Each share of Series A Preferred Stock shall entitle the holder thereof to a number of votes equal to the Multiplier Number then in effect on all matters submitted to a vote of stockholders of the Corporation.

(b) Except as otherwise provided herein or by law, the holders of shares of Series A Preferred Stock and the holders of shares of Common Stock shall vote together as a single class on all matters submitted to a vote of stockholders of the Corporation.

(c) (i) If at any time dividends on any Series A Preferred Stock shall be in arrears in an amount equal to six quarterly dividends thereon, the occurrence of such contingency shall mark the beginning of a period (herein called a “default period”) which shall extend until such time when all accrued and unpaid dividends for all previous quarterly dividend periods and for the current quarterly dividend period on all shares of Series A Preferred Stock then outstanding shall

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have been declared and paid or set apart for payment. During each default period, all holders of Series A Preferred Stock and any other series of Preferred Stock then entitled as a class to elect directors, voting together as a single class, irrespective of series, shall have the right to elect two Directors.

(ii) During any default period, such voting right of the holders of Series A Preferred Stock may be exercised initially at a special meeting called pursuant to Section 3(c)(iii) hereof or at any annual meeting of stockholders, and thereafter at annual meetings of stockholders; provided that neither such voting right nor the right of the holders of any other series of Preferred Stock, if any, to increase, in certain cases, the authorized number of Directors shall be exercised unless the holders of 10% in number of shares of Preferred Stock outstanding shall be present in person or by proxy. The absence of a quorum of holders of Common Stock shall not affect the exercise by holders of Preferred Stock of such voting right. At any meeting at which holders of Preferred Stock shall initially exercise such voting right, they shall have the right, voting as a class, to elect Directors to fill such vacancies, if any, in the Board of Directors as may then exist up to two Directors or, if such right is exercised at an annual meeting, to elect two Directors. If the number which may be so elected at any special meeting does not amount to the required number, the holders of the Preferred Stock shall have the right to make such increase in the number of Directors as shall be necessary to permit the election by them of the required number. After the holders of the Preferred Stock shall have exercised their right to elect Directors in any default period and during the continuance of such period, the number of Directors shall not be increased or decreased except by vote of the holders of Preferred Stock as herein provided or pursuant to the rights of any equity securities ranking senior to or pari passu with the Series A Preferred Stock.

(iii) Unless the holders of Preferred Stock shall have previously exercised their right to elect Directors during an existing default period, the Board of Directors may order, or any stockholder or stockholders owning in the aggregate not less than 10% of the total number of shares of Preferred Stock outstanding, irrespective of series, may request, the calling of a special meeting of holders of Preferred Stock, which meeting shall thereupon be called by the Chief Executive Officer, a Vice President or the Secretary of the Corporation. Notice of such meeting and of any annual meeting at which holders of Preferred Stock are entitled to vote pursuant to this Section 3(c)(iii) shall be given to each holder of record of Preferred Stock by mailing such notice to him at the address of such holder shown on the registry books of the Corporation or transfer agent or registrar for the Preferred Stock. Such meeting shall be called for a time not earlier than 20 days and not later than 60 days after such order or request or in default of the calling of such meeting within 60 days after

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such order or request, such meeting may be called on similar notice by any stockholder or stockholders owning in the aggregate not less than 10% of the total number of shares of Preferred Stock outstanding, irrespective of series. Notwithstanding the provisions of this Section 3(c)(iii), no such special meeting shall be called during the period within 60 days immediately preceding the date fixed for the next annual meeting of stockholders.

(iv) In any default period, the holders of Common Stock, and other classes of stock of the Corporation if applicable, shall continue to be entitled to elect the whole number of Directors until the holders of Preferred Stock shall have exercised their right to elect two Directors voting as a class, after the exercise of which right (x) the Directors so elected by the holders of Preferred Stock shall continue in office until their successors shall have been elected by such holders or until the expiration of the default period, and (y) any vacancy in the Board of Directors may (except as provided in Section 3(c)(ii) hereof) be filled by vote of a majority of the remaining Directors theretofore elected by the holders of the class of stock which elected the Director whose office shall have become vacant. References in this Section 3(c) to Directors elected by the holders of a particular class of stock shall include Directors elected by such Directors to fill vacancies as provided in clause (y) of the foregoing sentence.

(v) Immediately upon the expiration of a default period, (x) the right of the holders of Preferred Stock as a class to elect Directors shall cease, (y) the term of any Directors elected by the holders of Preferred Stock as a class shall terminate, and (z) the number of Directors shall be such number as may be provided for in the certificate of incorporation or bylaws irrespective of any increase made pursuant to the provisions of Section 3(c)(ii) (such number being subject, however, to change thereafter in any manner provided by law or in the certificate of incorporation or bylaws). Any vacancies in the Board of Directors effected by the provisions of clauses (y) and (z) in the preceding sentence may be filled by a majority of the remaining Directors.

(d) Except as otherwise expressly provided herein, holders of Series A Preferred Stock shall have no special voting rights and their consent shall not be required (except to the extent they are entitled to vote with holders of Common Stock as set forth herein) for taking any corporate action.

Section 4. Certain Restrictions. (a) Whenever quarterly dividends or other dividends or distributions payable on the Series A Preferred Stock as provided in Section 2 are in arrears, thereafter and until all accrued and unpaid dividends and distributions, whether or not declared, on outstanding shares of Series A Preferred Stock shall have been paid in full, the Corporation shall not:

(i) declare or pay dividends on, or make any other distributions on, any shares of Common Stock or other stock ranking junior (either as to dividends or upon liquidation, dissolution or winding-up) to the Series A Preferred Stock;

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(ii) declare or pay dividends on, or make any other distributions on, any shares of stock ranking on a parity (either as to dividends or upon liquidation, dissolution or winding-up) with the Series A Preferred Stock, except dividends paid ratably on the Series          Preferred Stock and all such other parity stock on which dividends are payable or in arrears in proportion to the total amounts to which the holders of all such shares are then entitled;

(iii) redeem, purchase or otherwise acquire for value any shares of Common Stock or other stock ranking junior (either as to dividends or upon liquidation, dissolution or winding-up) to the Series A Preferred Stock; provided that the Corporation may at any time redeem, purchase or otherwise acquire shares of any such junior stock in exchange for shares of stock of the Corporation ranking junior (as to dividends and upon dissolution, liquidation or winding-up) to the Series A Preferred Stock; or

(iv) redeem, purchase or otherwise acquire for value any shares of Series A Preferred Stock, or any shares of stock ranking on a parity (either as to dividends or upon liquidation, dissolution or winding-up) with the Series A Preferred Stock, except in accordance with a purchase offer made in writing or by publication (as determined in good faith by the Board) to all holders of Series A Preferred Stock and all such other parity stock upon such terms as the Board of Directors, after consideration of the respective annual dividend rates and other relative rights and preferences of the respective series and classes, shall determine in good faith will result in fair and equitable treatment among the respective series or classes.

(b) The Corporation shall not permit any subsidiary of the Corporation to purchase or otherwise acquire for value any shares of stock of the Corporation unless the Corporation could, under paragraph 4(a), purchase or otherwise acquire such shares at such time and in such manner.

Section 5. Reacquired Shares. Any shares of Series A Preferred Stock purchased or otherwise acquired by the Corporation in any manner whatsoever shall be retired and canceled promptly after the acquisition thereof. All such shares shall upon their cancellation become authorized but unissued shares of Preferred Stock without designation as to series and may be reissued as part of a new series of Preferred Stock to be created by resolution or resolutions of the Board of Directors subject to the conditions and any restrictions on issuance set forth herein or in the certificate of incorporation of the Corporation or as otherwise required by Delaware law.

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Section 6. Liquidation, Dissolution or Winding-up. Upon any liquidation, dissolution or winding-up of the Corporation, no distribution shall be made (a) to the holders of shares of stock ranking junior (either as to dividends or upon liquidation, dissolution or winding-up) to the Series A Preferred Stock unless, prior thereto, the holders of shares of Series A Preferred Stock shall have received an amount equal to accrued and unpaid dividends and distributions thereon, whether or not declared, to the date of such payment plus an amount equal to the greater of (i) $0.00001 per share or (ii) an aggregate amount per share equal to the Multiplier Number then in effect times the aggregate amount to be distributed per share to holders of Common Stock, or (b) to the holders of stock ranking on a parity (either as to dividends or upon liquidation, dissolution or winding-up) with the Series A Preferred Stock, except distributions made ratably on the Series A Preferred Stock and all such other parity stock in proportion to the total amounts to which the holders of all such shares are entitled upon such liquidation, dissolution or winding-up.

Section 7. Consolidation, Merger, etc. If the Corporation shall enter into any consolidation, merger, combination or other transaction in which the shares of Common Stock are exchanged for or changed into other stock or securities, cash or any other property, then in any such case the shares of Series A Preferred Stock shall at the same time be similarly exchanged for or changed into an amount per share equal to (x) the Multiplier Number then in effect times (y) the aggregate amount of stock, securities, cash or any other property, as the case may be, into which or for which each share of Common Stock is changed or exchanged. In the event that both this Section 7 and Section 2 appear to apply to a transaction, this Section 7 will control.

Section 8. No Redemption. The Series A Preferred Stock shall not be subject to redemption by the Corporation or at the option of any holder of Series A Preferred Stock; provided however that subject to Section 4(a)(iv), the Corporation may purchase or otherwise acquire outstanding shares of Series A Preferred Stock in the open market or by offer to any holder or holders of Series A Preferred Stock. The shares of Series A Preferred Stock shall not be subject to, or entitled to the operation of a retirement or sinking fund.

Section 9. Rank. The Series A Preferred Stock shall rank as to the payment of dividends and the distribution of assets upon liquidation, dissolution and winding-up junior to all other series of the Preferred Stock of the Corporation unless the Board of Directors shall specifically determine otherwise in fixing the powers, preferences and relative, participating, option and other special rights of the shares of such other series and the qualifications, limitations and restrictions thereof.

Section 10. Fractional Shares. Series A Preferred Stock may be issued in fractions of a share which shall entitle the holder, in proportion to such holder’s fractional shares, to exercise voting rights, receive dividends, participate in distributions and to have the benefit of all other rights of holders of Series A Preferred Stock.

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Section 11. Amendment. At any time when any shares of Series A Preferred Stock are outstanding, the certificate of incorporation of the Corporation shall not be amended in any manner (whether by merger or otherwise) which would alter or change the powers preferences and relative, participating, optional and other special rights of the Series A Preferred Stock so as to effect holders of the Series A Preferred Stock adversely, without the affirmative vote of the holders of at least two-thirds of the outstanding shares of Series A Preferred Stock, voting separately as a class.

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IN WITNESS WHEREOF, the undersigned has executed this Certificate of Designations this 9^th day of April, 2013.

[Signature Page to Certificate of Designations]