"One of the leading attorneys in the USA when it comes to the regulatory aspects of the purchase and sale of electric generation assets"
Chambers USA


Mark Williams represents clients that invest in the electric power and natural gas industries. He has advised private equity funds, insurance-sector investors, banks, pension funds, multinational institutional investors, hedge funds, and traditional investment funds on the complex regulatory requirements applicable to electricity and gas investments. He also advises on electricity and gas investments, financings, mergers, acquisitions, securities, and restructuring transactions.

Mark has represented investors in transactions totaling more than 44,000 MW of electric generating capacity, and more than 29,000 miles of natural gas pipeline capacity. He has protected the power sales eligibility and regulatory exemptions of renewable and high-efficiency Qualifying Facilities. He has advised buyers and sellers of generating company assets and interests on regulatory strategy and in formal application proceedings, and during the last decade, he has always had one or more M&A applications pending before FERC. He successfully represented private equity and insurance investors in former Enron electric facilities in FERC's 2003–2004 Enron proceedings, leading to the full and public exoneration of the clients. 

Before entering private practice, Mark was the sole attorney in the Division of Corporate Applications of the Federal Energy Regulatory Commission (FERC). In that role, he advised the commission on merger, divestiture, financing, independent power, and electrical transmission system matters, and led more than 100 commission orders in transactional-regulatory matters.

Mark also led FERC's review of generation facility sales, utility and holding company restructuring transactions, and a range of Regional Transmission Organization (RTO) proposals, including the acquisition of a US utility by a foreign energy system, and the independence of RTOs from other energy market participants.

Chambers USA recognized Mark as "one of the leading attorneys in the USA when it comes to the regulatory aspects of the purchase and sale of electric generation assets" and as "a tremendous resource for any team . . . well versed in regulatory minutiae and top of the class in the regulatory space." He is also recognized by Chambers Global and has been lead energy regulatory counsel to several project finance "deals of the year."

Prior to joining Mayer Brown, Mark was a partner in the energy practice of another international law firm.


Mark serves or has served as:

  • Energy regulatory counsel to Ares EIF Management LLC, the manager of leading electricity and gas private equity funds.
  • Energy regulatory counsel to Global Atlantic Financial Group and its portfolio of generating companies.
  • Energy regulatory counsel to Astoria Energy project companies in New York.
  • Energy regulatory counsel to financial and institutional creditors and noteholders of over 50 generating companies and holding companies, in connection with workout and restructuring matters.
  • Lead regulatory counsel to General Electric Energy Financial Services in connection with the financing, development, and regulation of new clean-energy wind-generation facilities across the country.
  • Lead regulatory counsel to AIG Highstar Capital in its 2002 acquisition of the 6,000-mile Southern Star Central gas pipeline (and to Southern Star in its 2003 refinancing, to AIG and Southern Star in the 2005 acquisition by General Electric Capital, and to Southern Star in its 2006 refinancing).


Columbia University, BA

New York Law School, JD


  • District of Columbia
  • New York


  • US Court of Appeals for the District of Columbia Circuit


  • Energy Bar Association: Vice Chair (2008–2010) and Chair (2010–2011) Committee on Professional Development and Ethics; Vice Chair, Chair-elect, and Chair, Committee on Finance and Transactions (2005–2007); Co-chair, Programs and Meetings Committee (2005–2006); Conference Chair, National Legislative Program (2005); Elected Member, Board of Directors (2002–2005); Founding Chair, Committee on Finance and Transactions (1999–2000); Chair, Committee on FERC Administration and Reorganization (1998–1999)
  • Trustee, Foundation of the Energy Law Journal (2011–2014)
  • Commissioner, City Industrial Development and Revenue Bond Authority, City of Alexandria, VA (Term 2002–2020; Chairman, 2012–2020)
  • Member, American Bar Association
  • Adviser to US Congress, House of Representatives, Subcommittee on Regulatory Reform and Paperwork Reduction (105th Congress) in connection with national electric-sector oversight hearings (1998)
  • Highly Regarded, IFLR1000 Financial and Corporate
  • Ranked, Energy: Electricity (Regulatory & Litigation) – USA, Chambers Global
  • Recommended, The Legal 500 US
  • Recognized, Project Finance Law, Washington, DC, The Best Lawyers in America
  • Ranked, Energy: Electricity (Regulatory & Litigation), Nationwide, Chambers USA
  • Highly Regarded, IFLR1000 United States
  • Leading Lawyer, IFLR1000 Financial and Corporate