Mr. Mercer represents clients before government agencies in environmental matters as well as litigation related to the development of natural resources and health care fraud and overpayments. To minimize the probability of civil or criminal liability for business entities, Mr. Mercer provides compliance counseling. He also represents companies and individuals in response to state and federal investigations and cases.

From June 2005 through July 2007, Mr. Mercer served as a senior Justice Department official in the positions of Acting Associate Attorney General and Principal Associate Deputy Attorney General. As Acting Associate Attorney General, he served as the third-ranking official in the DOJ and had oversight responsibilities for five litigating divisions (Antitrust, Civil, Civil Rights, Environment and Natural Resources and Tax) with criminal and civil cases.