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William Mercer


401 North 31st Street, Suite 1500, Billings, MT 59101

Bill relies on twenty-one years of government service to represent clients in litigation involving the federal government or the State of Montana, criminal and civil matters investigated by the federal government or the State of Montana, and federal and Montana regulatory matters.

His civil litigation and regulatory work is focused on environmental issues. Bill’s work on behalf of clients under government investigation is focused on allegations of violations of health care and environmental laws.

Bill previously served as a senior Justice Department official in the Bush Administration in two positions: Acting Associate Attorney General and Principal Associate Deputy Attorney General. As Associate Attorney General, he served as the third-ranking official in DOJ and had oversight responsibility for five litigating divisions (Antitrust, Civil, Civil Rights, Environment and Natural Resources and Tax) with criminal and civil cases. Bill served as United States Attorney in Montana from 2001 to 2009 and as an Assistant US Attorney from 1994 to 2001. In these roles, he was responsible for natural resources litigation, prosecution of criminal cases, and appellate practice on behalf of the United States.


False Claims Act

Bill defends clients against the risks of False Claims Act violations. He provides counsel  in every phase of qui tam proceedings under FCA - from the outset of the government’s investigation through trial. He also advises clients in related matters including regulatory reviews, debarment proceedings, and derivative suits.

  • United States Department of Justice and US Attorneys' Offices
  • Montana State District Courts
  • Montana Supreme Court
  • United States District Court in Montana
  • United States Court of Appeals for the Ninth Circuit
  • State of Montana Executive Branch agencies, particularly the Department of Environmental Quality
  • Montana Board of Environmental Review
  • United States Department of the Interior agencies, including the Bureau of Land Management and the Bureau of Indian Affairs

Client Results

  • In six years at the firm, Bill has managed teams and achieved optimal results for clients in cases involving the National Environmental Policy Act, the Montana Environmental Policy Act, the Montana Water Quality Act, the Montana Air Quality Act, federal and Montana criminal statutes and the False Claims Act, the Montana Consumer Protection Act, a rulemaking involving Montana’s numeric nutrient criteria, administrative enforcement actions, and a bid protest brought pursuant to the Montana Administrative Procedure Act.


Bar Admissions


  • Chambers USA, Natural Resources & Environment, 2016-2022
  • Mountain States Super Lawyers®, Environmental, 2022
  • The Best Lawyers in America©, Natural Resources Law, 2019-2022; Commercial Litigation, 2021, 2022
  • George Mason University School of Law, Distinguished Alumni Award

Professional and Civic Affiliations

  • University of Montana Foundation, Board of Trustees, Trustee
  • Billings Symphony Society, Board of Directors, Director
  • Big Sky Senior Services, Board of Directors, Director

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