We have acted as counsel to Dynegy Inc., a Delaware corporation (the "Company"), in connection with the preparation and filing under the Securities Act of 1933, as amended (the "Act") with the Securities and Exchange Commission (the "Commission") of the Company's Registration Statement on Form S-3ASR (the "Registration Statement") on the date hereof, including a base prospectus (the "Base Prospectus"), which provides that it will be supplemented by one or more prospectus supplements (each such prospectus supplement, together with the Base Prospectus, a "Prospectus"), relating to the registration (A) for issuance and sale by the Company of: (i) shares of common stock of the Company, par value $0.01 per share (the "Common Shares"), (ii) shares of preferred stock of the Company, par value $0.01 per share (the "Preferred Shares"), which may be convertible into or exchangeable for Common Shares or other securities of the Company, (iii) debt securities consisting of debentures, notes or other evidences of indebtedness representing unsecured obligations of the Company, which may be convertible into or exchangeable for Common Shares or other securities of the Company (the "Debt Securities"), (iv) guarantees of debt securities by the Company as guarantor (the "Guarantor") thereof (the "Guarantees"), (v) depositary shares representing fractional or multiple interests in Common Shares or Preferred Shares (the "Depositary Shares"), (vi) warrants to purchase Common Shares, Preferred Shares or Depositary Shares (the "Warrants"), (vii) contracts for the purchase or sale of Debt Securities, Preferred Shares, Common Shares or other securities (the "Purchase Contracts") and (viii) units of the Company consisting of one or more of the securities described in clauses (i) through (vii) above (the "Units") and (B) for the resale by the securityholder of the Company named in the Registration Statement under the caption "Selling Stockholders" (the "Selling Stockholder") of 19,541,152 shares of Common Shares (the "Selling Stockholder Common Shares"), in each case as contemplated in the Registration Statement to which this opinion is filed as an exhibit (as the same may be amended from time to time). The Common Shares, Preferred Shares, Debt Securities, Depositary Shares, Guarantees, Warrants, Purchase Contracts and Units are referred to herein collectively as the "Company Securities" and, together with the Selling Stockholder Common Shares, the "Securities." The Company Securities being registered under the Registration Statement will have an indeterminate aggregate initial offering price and will be offered on a continuous or delayed basis pursuant to the provisions of Rule 415 under the Act.


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In connection with the opinions expressed herein, we have reviewed the originals, or copies identified to our satisfaction, of corporate records, agreements, documents and other instruments, matters of law, proceedings and such certificates or comparable documents of public officials and of officers and representatives of the Company including: (i) the Company's Third Amended and Restated Certificate of Incorporation, as amended (the "Certificate of Incorporation"); (ii) the Company's Sixth Amended and Restated By-laws, as amended; (iii) the resolutions adopted by the Company's board of directors (the "Board") on September 28, 2017; (iv) the Registration Statement; (v) the Base Prospectus and (vi) the form of indenture (the "Indenture") between the Company and Wilmington Trust, National Association, as trustee (the "Trustee"), incorporated by reference as Exhibit 4.46 to the Registration Statement, and have made such inquiries of such officers and representatives as we have deemed relevant or necessary as a basis for the opinion hereinafter set forth. In such examination, we have assumed the genuineness of all signatures, the legal capacity of all natural persons, the authenticity of all documents submitted to us as originals, the conformity to original documents of all documents submitted to us as certified, conformed or photostatic copies, and the authenticity of the originals of such latter documents. As to all questions of fact material to this opinion that have not been independently established, we have relied upon certificates or comparable documents of officers and representatives of the Company and documents furnished to us by the Company without independent verification of their accuracy.

In rendering the opinions contained herein, we have assumed that: (i) the Registration Statement and any supplements and amendments thereto, will have become effective and will comply with all applicable laws (and will remain effective and in compliance at the time of issuance or resale of any Securities thereunder); (ii) a prospectus supplement describing each class or series of Securities offered pursuant to the Registration Statement, to the extent required by applicable law and relevant rules and regulations of the Commission, will be timely filed with the Commission and will comply with all applicable laws; (iii) the definitive terms of each class or series of Securities will have been established in accordance with the authorizing resolutions adopted by the Board (or an authorized committee thereof), the Certificate of Incorporation, and applicable law; (iv) the Company will issue and deliver the Company Securities in the manner contemplated by the Registration Statement including the applicable Prospectus and any Securities that consist of shares of capital stock will have been authorized and reserved for issuance, in each case within the limits of the then remaining authorized but unissued and unreserved amounts of such capital stock; (v) the resolutions authorizing the Company to issue, offer and sell the Securities will have been adopted by the Board (or an authorized committee thereof) and will be in full force and effect at all times at which the Securities are offered or sold by the Company; (vi) all Securities will be issued and sold in compliance with applicable federal and state securities laws or applicable laws or regulations or any agreement or other instrument binding upon the Company; and (vii) any Indenture, Deposit Agreement, Warrant Agreement, Purchase Contract Agreement or Unit Agreement (each as defined below) will be governed by and construed in accordance with the laws of the State of New York and will constitute a valid and binding obligation of each party thereto other than the Company.

With respect to any Company Securities consisting of Common Shares, we have further assumed that the Common Shares will be authorized, executed, countersigned by the transfer agent or registrar therefor and delivered by the Company in accordance with applicable laws and sold as contemplated in the Registration Statement.

With respect to any Company Securities consisting of any series of Preferred Shares, we have further assumed that: (i) the certificate of designations, approved by us, relating to the Preferred Shares establishing the designations, preferences and rights of the class or series of Preferred Shares (the "Certificate of Designations"), will have been authorized, executed and filed with the Secretary of State of the State of Delaware, (ii) the Preferred Shares will be authorized, executed, countersigned by the registrar and transfer agent therefor and delivered by the Company in accordance with the provisions of the Certificate of Designations and applicable laws and sold as contemplated in the


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Registration Statement, (iii) if the Preferred Shares are convertible into Common Shares or other securities of the Company, (x) such Common Shares or other securities of the Company will be authorized, (y) the Preferred Shares will be presented for conversion in accordance with the terms thereof and (z) such Common Shares or other securities of the Company will be executed, countersigned by the transfer agent therefor and delivered by the Company upon such conversion, in accordance with the terms of such Preferred Shares.

With respect to any Company Securities consisting of any series of Debt Securities, we have further assumed that: (i) that the Indenture will have been authorized, executed and delivered by the Company and the Trustee, (ii) the Debt Securities will be issued pursuant to the Indenture, (iii) all terms of the Debt Securities not provided for in the Indenture will have been established in accordance with the provisions of the Indenture and reflected in appropriate documentation approved by us and, if applicable, executed and delivered by the Company and authenticated by the Trustee, (iv) the Debt Securities will be authorized, executed, authenticated, issued and delivered by the Company and the Trustee in accordance with the provisions of the Indenture and applicable laws and sold as contemplated in the Registration Statement and (v) if the Debt Securities are convertible into Common Shares or other securities of the Company, (x) such Common Shares or other securities of the Company will be authorized, (y) the Debt Securities will be presented for conversion in accordance with the terms thereof and (z) such Common Shares or other securities of the Company will be executed, countersigned by the transfer agent therefor and delivered by the Company upon such conversion, in accordance with the terms of such Debt Securities.

With respect to any Company Securities consisting of Guarantees, we have further assumed that the issuance of the Guarantee will be authorized, executed, issued and delivered by the Company in accordance with applicable laws and sold as contemplated in the Registration Statement.

With respect to any Company Securities consisting of Depositary Shares, we have further assumed that: (i) the deposit agreement, approved by us, relating to the Depositary Shares (the "Deposit Agreement") to be entered into between the Company and an entity selected by the Company to act as depository (the "Depositary") will have been authorized, executed and delivered by the Company and the Depositary, (ii) the Company will deposit with the Depositary, Common Shares or Preferred Shares to be represented by the Depositary Shares that are authorized, validly issued and delivered as contemplated by the Registration Statement including the applicable Prospectus and the Deposit Agreement and (iii) the Depositary Shares will be authorized, executed, issued, fully-paid and delivered by the Company and the Depositary in accordance with the provisions of the Deposit Agreement and applicable laws and sold as contemplated in the Registration Statement.

With respect to any Company Securities consisting of any series of Warrants, we have further assumed that: (i) the warrant agreement, approved by us, relating to the Warrants (the "Warrant Agreement") to be entered into between the Company and an entity selected by the Company to act as the warrant agent (the "Warrant Agent") will have been authorized, executed and delivered by the Company and the Warrant Agent and (ii) the Warrants will be authorized, executed, authenticated, issued and delivered by the Company and the Warrant Agent in accordance with the provisions of the Warrant Agreement and applicable laws and sold as contemplated in the Registration Statement.

With respect to any Company Securities consisting of Purchase Contracts, we have further assumed that: (i) the purchase contract agreement, approved by us, relating to the Purchase Contracts (the "Purchase Contract Agreement") to be entered into between the Company and an entity selected by the Company to act as the purchase contract agent (the "Purchase Contract Agent") will have been authorized, executed and delivered by the Company and the Purchase Contract Agent and (ii) the Purchase Contracts will be authorized, executed, authenticated, issued and delivered by the Company and the Purchase Contract Agent in accordance with the provisions of the Purchase Contract Agreement and applicable law and sold as contemplated in the Registration Statement.


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With respect to any Company Securities consisting of Units, we have further assumed that (i) the unit agreement, approved by us, relating to the Units (the "Unit Agreement") to be entered into between the Company and an entity selected by the Company to act as the unit agent (the "Unit Agent") will have been authorized, executed and delivered by the Company and the Unit Agent and (ii) the Units and each component of the Units will be authorized, executed, authenticated, issued, fully paid and non-assessable (to the extent applicable) and delivered by the Company and the Unit Agent in accordance with the provisions of the Unit Agreement and applicable laws and sold as contemplated in the Registration Statement and each component of the Units will constitute a valid and binding obligation of the Company or any third party (to the extent applicable) as contemplated by the Registration Statement including the applicable Prospectus and the Unit Agreement.

Based on the foregoing, and subject to the qualifications, assumptions and limitations stated herein, we are of the opinion that:


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Our opinions expressed above are subject to the qualifications that we express no opinion as to the applicability of, compliance with, or effect of any laws except the laws of the State of New York, the General Corporation Law of the State of Delaware and the Federal laws of the United States of America.

We hereby consent to the filing of this opinion with the Commission as Exhibit 5.1 to the Registration Statement. We also consent to the reference to our firm under the heading "Legal Matters" in the Registration Statement. In giving this consent, we do not thereby admit that we are in the category of persons whose consent is required under Section 7 of the Act or the rules and regulations of the Commission promulgated thereunder.

The opinions set forth in this letter are effective as of the date hereof. We do not undertake to advise you of any changes in our opinion expressed herein resulting from matters that may arise after the date of this letter or that hereinafter may be brought to our attention. We express no opinions other than as herein expressly set forth, and no opinion may be inferred or implied beyond that expressly stated herein.