Exhibit 5.1

December 13, 2021

Babcock & Wilcox Enterprises, Inc.

1200 East Market Street, Suite 650

Akron, OH 44305

Ladies and Gentlemen:

We have acted as special counsel to Babcock & Wilcox Enterprises, Inc., a Delaware corporation (the “Company”), in connection with the issuance and sale of $140,000,000 aggregate principal amount of the Company’s 6.50% Senior Notes due 2026 (the “Notes”), pursuant to that certain Underwriting Agreement, dated December 8, 2021 (the “Underwriting Agreement”), between the Company and B. Riley Securities, Inc., as representative of the several underwriters listed in Schedule 1 to the Underwriting Agreement. The Notes constitute a series of the debt securities registered on a Registration Statement on Form S-3 (File No. 333-260854) (the “Registration Statement”), filed by the Company with the Securities and Exchange Commission (the “Commission”) under the Securities Act of 1933, as amended (the “Securities Act”) on November 8, 2021 and declared effective by the Commission on November 22, 2021. The Notes are to be issued pursuant to the terms and conditions of, and in the form set forth in, the Indenture entered into by and between the Company and The Bank of New York Mellon Trust Company National Association, as trustee (the “Trustee”), dated as of February 12, 2021 (as supplemented by that First Supplemental Indenture, dated as of February 12, 2021 between the Company and the Trustee, the “Base Indenture”), as supplemented by the Second Supplemental Indenture, dated as of December 13, 2021 (the “Supplemental Indenture” and, together with the Base Indenture, the “Indenture”), between the Company and the Trustee.

In connection with the opinions expressed herein, we have examined originals or copies, certified or otherwise identified to our satisfaction, of such documents, records and matters of law as we have deemed relevant or necessary for purposes of this opinion. In our examination, we have assumed that the certificates for the Notes will conform to the form thereof examined by us, the legal capacity of all natural persons, the genuineness of all signatures, the authenticity of all documents submitted to us as originals, the conformity to original documents of all documents submitted to us as copies and the authenticity of the originals of such copies. To the extent the Company’s obligations depend on the enforceability of any agreement against the other parties to such agreement, we have assumed that such agreement is enforceable against such other parties. As to any facts material to the opinions expressed herein which were not independently established or verified, we have relied upon oral or written statements and representations of officers and other representatives of the Company. In addition, we have obtained and relied upon those certificates of public officials we considered appropriate.

On the basis of such examination, our reliance upon the assumptions in this opinion and our consideration of those questions of law we considered relevant, and subject to the limitations and qualifications in this opinion, we are of the opinion that the issuance of the Notes has been duly authorized by all necessary corporate action on the part of the Company and, upon payment for and delivery of the Notes in accordance with the Underwriting Agreement and the authentication of the certificates representing the Notes by a duly authorized signatory of the Trustee in accordance with the Indenture, the Notes will be legally valid and binding obligations of the Company, enforceable against the Company in accordance with their terms, except as may be limited (a) by bankruptcy, insolvency, reorganization, moratorium or similar laws relating to or affecting creditors’ rights generally (including, without limitation, fraudulent conveyance laws) and (b) by general principles of equity including, without limitation, concepts of materiality, reasonableness, good faith and fair dealing and the possible unavailability of specific performance or injunctive relief, regardless of whether considered in a proceeding at law or in equity.

The law covered by this opinion is limited to the present law of the State of New York and the current General Corporation Law of the State of Delaware. We express no opinion as to the laws of any other jurisdiction and no opinion regarding the statutes, administrative decisions, rules, regulations or requirements of any county, municipality, subdivision or local authority of any jurisdiction.

This opinion is being furnished in accordance with the requirements of Item 601(b)(5) of Regulation S-K promulgated under the Securities Act, as amended, or the rules and regulations of the Commission promulgated thereunder, and no opinion is expressed herein as to any matter pertaining to the contents of the Registration Statement, the prospectus included in the Registration Statement or any prospectus supplement, other than as expressly stated herein with respect to the Notes.

We hereby consent to the filing of this opinion as Exhibit 5.1 to the Company’s Current Report on Form 8-K dated the date hereof filed by the Company and incorporated by reference into the Registration Statement, and to the reference to O’Melveny & Myers LLP under the heading “Legal Matters” in the prospectus supplement, dated December 8, 2021, constituting a part of such Registration Statement. In giving such consent, we do not admit that we are in the category of persons whose consent is required under Section 7 of the Securities Act or the rules and regulations of the Commission thereunder.

Respectfully submitted,

/s/ O’Melveny & Myers LLP