Exhibit 3.1

SECOND AMENDED AND RESTATED

CERTIFICATE OF INCORPORATION

OF

HARMONY MERGER CORP.

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Pursuant to Sections 242 and 245 of the

Delaware General Corporation Law

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 HARMONY MERGER CORP., a corporation existing under the laws of the State of Delaware (the “Corporation”), by its Chief Executive Officer, hereby certifies as follows:

1. The name of the Corporation is “Harmony Merger Corp.”

2. The Corporation’s Certificate of Incorporation was filed in the office of the Secretary of State of the State of Delaware on May 21, 2014.

3. The Corporation first amended and restated its Certificate of Incorporation on March 23, 2015 and subsequently amended such first amended and restated Certificate of Incorporation on March 27, 2017 (such amended and restated Certificate of Incorporation, as amended, being referred to herein as the “First Amended and Restated Certificate of Incorporation”).

4. This Second Amended Restated Certificate of Incorporation restates, integrates and amends the First Amended and Restated Certificate of Incorporation of the Corporation.

5. This Second Amended and Restated Certificate of Incorporation was duly adopted by the directors and stockholders of the Corporation in accordance with the applicable provisions of Sections 242 and 245 of the General Corporation Law of the State of Delaware, as amended (the “DGCL”).

6. The text of the First Amended and Restated Certificate of Incorporation of the Corporation is hereby amended and restated to read in full as follows:

FIRST: The name of the corporation is NextDecade Corporation (hereinafter sometimes referred to as the “Corporation”).

SECOND: The registered office of the Corporation is to be located at 850 New Burton Road, Suite 201, Dover, Delaware 19904, Kent County. The name of its registered agent at that address is Cogency Global Inc.

THIRD: The purpose of the Corporation shall be to engage in any lawful act or activity for which corporations may be organized under the DGCL. In addition to the powers and privileges conferred upon the Corporation by law and those incidental thereto, the Corporation shall possess and may exercise all the powers and privileges that are necessary or convenient to the conduct, promotion or attainment of the business or purposes of the Corporation.

FOURTH: The total number of shares of all classes of capital stock which the Corporation shall have authority to issue is 481,000,000, of which 480,000,000 shares shall be common stock of the par value $.0001 per share (“Common Stock”) and 1,000,000 shares shall be preferred stock of the par value of $.0001 per share (“Preferred Stock”).

A. Preferred Stock. The Board of Directors is expressly granted authority to issue shares of the Preferred Stock, in one or more series, and to fix for each such series such voting powers, full or limited, and such designations, preferences and relative, participating, optional or other special rights and such qualifications, limitations or restrictions thereof as shall be stated and expressed in the resolution or resolutions adopted by the Board of Directors providing for the issue of such series (a “Preferred Stock Designation”) and as may be permitted by the DGCL. The number of authorized shares of Preferred Stock may be increased or decreased (but not below the number of shares thereof then outstanding) by the affirmative vote of the holders of a majority of the voting power of all of the then outstanding shares of the capital stock of the Corporation entitled to vote generally in the election of directors, voting together as a single class, without a separate vote of the holders of the Preferred Stock, or any series thereof, unless a vote of any such holders is required pursuant to any Preferred Stock Designation.

B. Common Stock. (1) Except as otherwise required by law or as otherwise provided in any Preferred Stock Designation, the holders of the Common Stock shall exclusively possess all voting power and each share of Common Stock shall have one vote.

(2) Subject to the prior rights of all classes or series of stock at the time outstanding having prior rights as to dividends or other distributions, the holders of shares of Common Stock shall be entitled to receive such dividends and other distributions in cash, property, or stock as may be declared on the Common Stock by the Board of Directors from time to time out of assets or funds of the Corporation legally available therefor and shall share equally on a per share basis in all such dividends and other distributions.

(3) Subject to the prior rights of creditors of the Corporation and the holders of all classes or series of stock at the time outstanding having prior rights as to distributions upon liquidation, dissolution or winding up of the Corporation, in the event of any liquidation, dissolution or winding up of the Corporation, either voluntary or involuntary, the holders of shares of Common Stock shall be entitled to receive their ratable and proportionate share of the remaining assets of the Corporation.

(4) No holder of shares of Common Stock shall have cumulative voting rights.

(5) No holder of shares of Common Stock shall be entitled to preemptive or subscription rights pursuant to this Second Amended and Restated Certificate of Incorporation.

C. Power to Sell and Purchase Shares. Subject to the requirements of applicable law, the Corporation shall have the power to issue and sell all or any part of any shares of any class of stock herein or hereafter authorized to such persons, and for such consideration and for such corporate purposes, as the Board of Directors shall from time to time, in its discretion, determine, whether or not greater consideration could be received upon the issue or sale of the same number of shares of another class, and as otherwise permitted by law. Subject to the requirements of applicable law, the Corporation shall have the power to purchase any shares of any class of stock herein or hereafter authorized from such persons, and for such consideration and for such corporate purposes, as the Board of Directors shall from time to time, in its discretion, determine, whether or not less consideration could be paid upon the purchase of the same number of shares of another class, and as otherwise permitted by law.

FIFTH: A. Number of Directors. Upon the effectiveness of this Second Amended and Restated Certificate of Incorporation (the “Effective Time”), the total number of directors constituting the entire Board of Directors shall be nine (9). Thereafter, the total number of directors constituting the entire Board of Directors shall be such number as may be fixed from time to time exclusively by resolution adopted by the affirmative vote of at least a majority of the Board of Directors then in office.

B. Classification. Subject to the terms of any one or more series of Preferred Stock, and effective upon the Effective Time, the Board of Directors shall be divided into three classes: Class A, Class B and Class C. The number of directors in each class shall be as nearly equal as possible. The Board of Directors may assign members of the Board of Directors already in office to such classes as of the Effective Time. The directors in Class A shall be elected for a term expiring at the first Annual Meeting of Stockholders after the Effective Time, the directors in Class B shall be elected for a term expiring at the second Annual Meeting of Stockholders after the Effective Time, and the directors in Class C shall be elected for a term expiring at the third Annual Meeting of Stockholders after the Effective Time.

C. Term and Filling Vacancies. Commencing at the first Annual Meeting of Stockholders after the Effective Time and at each annual meeting thereafter, directors elected to succeed those directors whose terms expire shall be elected for a term of office to expire at the third succeeding Annual Meeting of Stockholders after their election. Except as the DGCL may otherwise require, in the interim between Annual Meetings of Stockholders or Special Meetings of Stockholders called for the election of directors and/or the removal of one or more directors and the filling of any vacancy in that connection, newly created directorships and any vacancies in the Board of Directors, including unfilled vacancies resulting from the removal of directors for cause, may be filled by the vote of a majority of the remaining directors then in office, although less than a quorum (as defined in the Corporation’s by-laws), or by the sole remaining director. All directors shall hold office until the expiration of their respective terms of office and until their successors shall have been elected and qualified. A director elected to fill a vacancy resulting from the death, resignation or removal of a director shall serve for the remainder of the full term of the director whose death, resignation or removal shall have created such vacancy and until his successor shall have been elected and qualified. If the number of directors is changed, any increase or decrease shall be apportioned among the classes in a manner as the Board of Directors shall determine so as to maintain the number of directors in each class as nearly equal as possible, but in no cases will an increase or decrease in the number of directors shorten the term of an incumbent.

D. Election. Election of directors need not be by written ballot unless the by-laws of the Corporation so provide.

E. Officers. Except as otherwise expressly delegated by resolution of the Board of Directors, the Board of Directors shall have the exclusive power and authority to appoint and remove officers of the Corporation.

SIXTH: The following provisions are inserted for the management of the business and for the conduct of the affairs of the Corporation, and for further definition, limitation and regulation of the powers of the Corporation and of its directors and stockholders:

A. Powers of the Board of Directors. The business and affairs of the Corporation shall be managed by or under the direction of the Board of Directors. In addition to the powers and authorities hereinbefore or by statute expressly conferred upon them, the directors are hereby empowered to exercise all such powers and do all such acts and things as may be exercised or done by the Corporation; subject, nevertheless, to the provisions of the statutes of Delaware, of this Second Amended and Restated Certificate of Incorporation, and to any by-laws from time to time made by the stockholders; provided, however, that no by-law so made shall invalidate any prior act of the directors which would have been valid if such by-law had not been made.

B. By-laws. The Board of Directors shall have the power, without the assent or vote of the stockholders, to make, alter, amend, change, add to or repeal the by-laws of the Corporation as provided in the by-laws of the Corporation.

C. Special Meetings. Subject to the terms of any one or more series or classes of Preferred Stock, Special Meetings of the Stockholders of the Corporation may be called as prescribed by the by-laws of the Corporation.

SEVENTH: A. To the fullest extent permitted by the DGCL, as the same exists or as may hereafter be amended, a director of the Corporation shall not be personally liable to the Corporation or its stockholders for monetary damages for breach of fiduciary duty as a director. If the DGCL is amended to authorize corporate action further eliminating or limiting the personal liability of directors, then the liability of a director of the Corporation shall be eliminated or limited to the fullest extent permitted by the DGCL, as so amended. Any alteration, amendment, addition to or repeal of this Article Seventh, or adoption of any provision of this Second Amended and Restated Certificate of Incorporation (including any certificate of designations relating to any series or class of Preferred Stock) inconsistent with this Article Seventh, shall not reduce, eliminate or adversely affect any right or protection of a director of the Corporation existing at the time of such alteration, amendment, addition to, repeal or adoption with respect to acts or omissions occurring prior to such alteration, amendment, addition to, repeal or adoption.

B. As more fully prescribed in the by-laws, the Corporation shall indemnify and provide advancement to any indemnitee to the fullest extent permitted by law, as such may be amended from time to time.

C. Notwithstanding the foregoing provisions of this Article Seventh, no indemnification nor advancement of expenses will extend to any claims made by the Company’s officers and directors to cover any loss that such individuals may sustain as a result of such individuals’ agreement to pay debts and obligations to target businesses or vendors or other entities that are owed money by the Corporation for services rendered or contracted for or products sold to the Corporation, as described in the Registration Statement.

EIGHTH: No action that is required or permitted to be taken by the stockholders of the Corporation at any annual or special meeting of stockholders may be effected by written consent of stockholders in lieu of a meeting.

NINTH: A. In anticipation that York Capital Management, L.P., York Credit Opportunities Fund, L.P., York Select, L.P., Valinor Capital Partners SPV XIX, LLC, Valinor Capital Partners SPV XXII, LLC, VND Partners, L.P., Halcyon Energy, Power, and Infrastructure Capital Holdings LLC, Halcyon Mount Bonnell Fund L.P., GE Oil & Gas, Inc., and/or each of their respective affiliates (each, an “Investor” and collectively, the “Investors”) will be, indirectly or directly, substantial stockholders of the Corporation, and in recognition of (i) the benefits to be derived by the Corporation through its continued contractual, corporate and business relations with each Investor (including service of officers, directors, partners, managers, employees or affiliates of each Investor (collectively, “Investor Persons”) as directors of the Corporation) and (ii) the difficulties attendant to any director, who desires and endeavors fully to satisfy such director’s fiduciary duties, in determining the full scope of such duties in any particular situation, the provisions of this Article Ninth are set forth to regulate, define and guide the conduct of certain affairs of the Corporation as they may involve the Investors and any Investor Persons, and the powers, rights, duties and liabilities of the Corporation and its officers, directors and stockholders in connection therewith.

B. Except as the Investors may otherwise agree in writing, each Investor shall have the right to (i) engage, directly or indirectly, in the same or similar business activities or lines of business as the Corporation and (ii) do business with any client, competitor or customer of the Corporation, with the result that the Corporation shall have no right in or to such activities or any proceeds or benefits therefrom and no Investor or Investor Person (except as provided in paragraph (C) of this Article Ninth) shall be liable to the Corporation or its stockholders for breach of any fiduciary duty by reason of any such activities of such Investor or such Investor Person’s participation therein. In the event that any Investor or Investor Person acquires knowledge of a potential transaction or matter that may be a corporate opportunity for both the Corporation and such Investor, such Investor or Investor Person shall have no duty to communicate or present such corporate opportunity to the Corporation and the Corporation hereby renounces any interest or expectancy it may have in such corporate opportunity, with the result that such Investor or Investor Person shall not be liable to the Corporation or its stockholders for breach of any fiduciary duty, including for breach of any fiduciary duty as a stockholder of the Corporation by reason of the fact that such Investor pursues or acquires such corporate opportunity for itself, directs such corporate opportunity to another person or entity, or does not present such corporate opportunity to the Corporation.

C. In the event that a director or officer of the Corporation who is an Investor Person acquires knowledge of a potential transaction or matter that may be a corporate opportunity for both the Corporation and any Investor, such corporate opportunity shall belong to such Investor, and the Corporation hereby renounces any interest or expectancy it may have in such corporate opportunity, unless such corporate opportunity is expressly offered to such director or officer in his capacity as a director or officer of the Corporation, in which case such corporate opportunity shall belong to the Corporation.

D. For the purposes of this Article Ninth, “corporate opportunities” shall not include any business opportunities that the Corporation is not financially or contractually able to undertake, or that are, from their nature, not in the line of the Corporation’s business or are of no practical advantage to it or that are ones in which the Corporation has no interest or reasonable expectancy.

E. Any person or entity purchasing or otherwise acquiring any interest in any shares of capital stock of the Corporation shall be deemed to have had notice of and consented to the provisions of this Article Ninth.

F. For purposes of this Article Ninth only, the “Corporation” shall mean the Corporation and all corporations, partnerships, joint ventures, associations and other entities in which the Corporation beneficially owns (directly or indirectly) fifty percent (50%) or more of the outstanding voting stock, voting power, or similar voting interests.

TENTH. A. Forum. Unless the Corporation consents in writing in advance to the selection of an alternative forum, the Court of Chancery of the State of Delaware shall, to the fullest extent permitted by law, be the sole and exclusive forum for (A) any derivative action or proceeding brought on behalf of the Corporation, (B) any action asserting a claim of breach of a fiduciary duty owed by, or any wrongdoing by, any director, officer or employee of the Corporation to the Corporation or the Corporation’s stockholders, (C) any action asserting a claim arising pursuant to any provision of the DGCL, this Second Amended and Restated Certificate of Incorporation (including as it may be amended from time to time), or the by-laws, (D) any action to interpret, apply, enforce or determine the validity of this Second Amended and Restated Certificate of Incorporation or the by-laws, or (E) any action asserting a claim governed by the internal affairs doctrine, except for, as to each of (A) through (E) above, any claim as to which the Court of Chancery determines that there is an indispensable party not subject to the personal jurisdiction of the Court of Chancery (and the indispensable party does not consent to the personal jurisdiction of the Court of Chancery within ten (10) days following such determination). To the fullest extent permitted by law, any person or entity purchasing or otherwise acquiring or holding any interest in shares of capital stock of the Corporation shall be deemed to have notice of and consented to the provisions of this Article Tenth.

B. Amendment. The Corporation reserves the right, at any time and from time to time, to alter, amend, add to or repeal any provision contained in this Second Amended and Restated Certificate of Incorporation (including any certificate of designations relating to any series or class of Preferred Stock) in any manner now or hereafter prescribed by the laws of the State of Delaware, and all rights, preferences, privileges and powers of any nature conferred upon stockholders, directors or any other persons herein are granted subject to this reservation.

C. Severability. If any provision (or any part thereof) of this Second Amended and Restated Certificate of Incorporation shall be held to be invalid, illegal or unenforceable as applied to any circumstance for any reason whatsoever: (i) the validity, legality and enforceability of such provisions in any other circumstance and of the remaining provisions of this Second Amended and Restated Certificate of Incorporation including, without limitation, each portion of any section of this Certificate containing any such provision held to be invalid, illegal or unenforceable that is not itself held to be invalid, illegal or unenforceable) shall not in any way be affected or impaired thereby and (ii) to the fullest extent possible, the provisions of this Certificate (including, without limitation, each such containing any such provision held to be invalid, illegal or unenforceable) shall be construed so as to permit the Corporation to protect its directors, officers, employees and agents from personal liability in respect of their good faith service or for the benefit of the Corporation to the fullest extent permitted by law.

IN WITNESS WHEREOF, the Corporation has caused this Second Amended and Restated Certificate of Incorporation to be signed by Kathleen Eisbrenner, its Chief Executive Officer, as of the 24^th day of July, 2017.

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