William L. Thomas is counsel and head of the firm’s Environment, Health & Safety Practice. Bill advises companies, financiers, developers and other enterprises on environmental law matters, including transactions, projects, and formulation of management and legal compliance strategy. He also handles litigation and disputes involving environmental, health and safety concerns. His expertise in international environmental law and policy matters includes analyzing risks and opportunities arising under regional and international environmental agreements, requirements under emerging EHS legal regimes and related international standards and codes of conduct, and legal aspects of sustainability, corporate social responsibility, and Environmental, Social, Governance (ESG) matters.

Bill is also highly regarded in the area of climate change law, policy and strategy. Specific experience in this field includes: conducting greenhouse gas (GHG) due diligence, applying carbon and other environmental standards and drafting and negotiating related provisions in transactional and financing documents in connection with mergers, acquisitions, financing of projects and other ventures. He also advises clients on international, federal and state GHG regimes and initiatives and counsels companies, utilities and financiers on emissions trading activities, GHG emission reduction projects, voluntary carbon market issues and related governance matters, including policies, management systems, disclosures, and offsetting activities.

Bill is ranked in Band 1 for Environmental (Transactional) by Chambers USA (2022). He is also consistently ranked among the leading individuals practicing in the area of environmental law by The Best Lawyers in America, The International Who's Who of Environmental Lawyers, The Euromoney Energy and Environment Expert Guide, and Super Lawyers (DC), among others. In addition to his role as a Regent of the American College of Environmental Lawyers, Bill is a fellow in the American Bar Foundation and serves in a number of other appointments, including the Leadership Council of the Environmental Law Institute, the External Advisory Board of the Graham Sustainability Institute at the University of Michigan, and the Advisory Board of the Environmental Law Institute's Environmental Law Reporter.

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Prior to joining Willkie, Bill was with Skadden, Arps, Slate, Meagher & Flom LLP, and was Americas Environment Head for Clifford Chance LLP.

Bill is a member of the American Bar Association’s Sections on Environment, Energy and Resources (SEER) and International Law (SIL), having previously served on the governing Council for both sections, as well as past Chair of the International Environmental Law committees of both SEER and SIL. He is also a member of the International Bar Association, the American Society of International Law, and the IUCN Commission on Environmental Law.

Bill serves as a member of several other bodies, including the Strategic Advisory Counsel of the Erb Institute for Global Sustainable Enterprise (a partnership between the School of Natural Resources and Environment and the Stephen M. Ross School of Business at the University of Michigan), the External Advisory Board of the Graham Environmental Sustainability Institute at the University of Michigan, the Advisory Committee to the Carbon Disclosure Standards Board, and the U.S. Advisory Council to the Carbon Disclosure Project.

Bill appears frequently at national and international conferences, and is a widely published author on environmental law, policy and related matters of corporate strategy. In 2007, he served as Chair of ABA SEER's annual Conference on Environmental Law in Keystone, Colorado. In 2016, Bill was selected to serve on Law360’s Environmental Editorial Advisory Board.

Bill’s body of published work includes contributions to the Cross-Border Environment Handbook (PLC 2010/11), Stumbling Toward Sustainability (John Dernbach ed., ELI 2002), and Environmental Law and Enforcement in the Asia-Pacific Rim (Terri Mottershead ed., Sweet & Maxwell 2002).

Bill's articles on environmental issues have appeared in The National Law Journal, Natural Resources & Environment, Review of European Community & International Environmental Law, The International Lawyer, International Financial Law Review, Georgetown International Environmental Law Review, BNA's Environmental Law Reporter, European Environmental Law Review, Corporate Environmental Strategy, Project Finance International, Carbon Business and Environmental Finance, among others. He also serves on several editorial advisory boards, including those of BNA's Environmental Due Diligence Guide, Carbon & Climate Law Review, Sustainable Development Law & Policy, and Environmental Liability.

  • Brookfield Business Partners in its acquisition of Westinghouse Electric Company

  • Mueller Industries, Inc. in its acquisition of ATCO Rubber products

  • CapStreet Group in its acquisition of CRS Texas

  • Safe Fleet Holdings LLC, a portfolio company of long-term private equity sponsor client The Sterling Group, in its sale to Oak Creek Capital Partners

  • W&W|AFCO Steel in its acquisition of Hirschfeld Industries

  • Alleghany Capital Corporation in its majority investment in W&W|AFCO Steel

  • Meadow Partners and Trammell Crow Company (TCC) in their joint acquisition of an 80 percent condominium interest in the Motion Picture Association of America (MPAA) Building, located at 888 16th Street, NW in downtown Washington, DC.

  • Dubin Clark & Company, Inc. in series of acquisitions of U.S. based event rental and productions companies

  • FFL Partners in acquisition of Icynene, Inc., an international producer and supplier of residential and commercial foam insulation products

  • FFL Partners in its acquisition of Iracore, a manufacturer of specialized industrial pipes for the oilfield industry

  • Calvert Street Capital Partners in its sale of IOS Holdings, a U.S. oilfield inspection and services business, to LB Foster

  • Mueller Industries, Inc. and Atlas Holdings LLC in the acquisition of Tecumseh Products 



Georgetown University Law Center, J.D., 1989 St. Olaf College, B.A., 1986

Bar Admissions

District of Columbia New York