Peter D. Keisler

Peter D. Keisler

Partner, Sidley Austin LLP

PETER D. KEISLER is a former Acting Attorney General of the United States, a co-leader of Sidley’s Supreme Court and Appellate practice and a member of the firm’s Executive Committee. Peter has successfully represented some of the country’s largest companies in the telecommunications, transportation, energy and healthcare industries, as well as a host of national trade associations, providing extensive insight and experience gained from his more than 30 years of private and public sector experience.  

Including him in its top tier of the nation’s appellate lawyers, Chambers USA 2019 remarks that Peter is “regarded among fellow appellate practitioners as a ‘very talented and incredibly polished oral advocate’ who is ‘careful, brilliant and all-around amazing.’”

Peter has argued a wide range of federal constitutional, statutory and administrative law cases. His practice representing clients before the U.S. Supreme Court, federal courts of appeals and federal district courts has included the leading role in the nation’s most important and successful commercial and regulatory cases of the past several years, including United States of America v. AT&T & Time Warner, UARG v. EPA, and AEP v. Connecticut. United States of America v. AT&T & Time Warner was one of the most prominent antitrust cases in recent memory. Peter successfully represented AT&T in the Justice Department’s appeal of the District Court decision rejecting the government’s attempt to enjoin AT&T’s acquisition of Time Warner. This was the first time in more than four decades that the government litigated to judgment a challenge to a vertical merger. 

Peter’s arguments before the U.S. Supreme Court include:

  • Utility Air Regulatory Group v. Environmental Protection Agency (UARG v. EPA). Peter successfully argued that the EPA has no authority to impose permitting obligations on a source based solely on its emissions of greenhouse gases.
  • American Electric Power Co. v. Connecticut. Peter successfully represented four utility companies in this case, in which the Court unanimously reversed the court of appeals and held that states and private parties could not seek judicially imposed reductions in greenhouse gas emissions against electric utilities under a federal common-law nuisance theory. The leading Supreme Court blog called this litigation “the biggest-ever case on the issue of global warming” and AmLaw Media named Peter its “Appellate Lawyer of the Week” for the argument, calling the case “one of the biggest environmental cases of the decade, if not the century.”
  • National Cable & Telecommunications Association v. Gulf Power. Peter successfully argued on behalf of the cable television industry in this case, in which the Court held that cable operators offering high-speed Internet service are entitled to access to electric utility poles at regulated rates.
  • Roberts v. Sea-Land Services, Inc. Peter successfully argued on behalf of the respondent in this case involving the construction and application of federal worker compensation laws.

Peter is widely recognized as a leader in his field. He is consistently named as a leading appellate lawyer by Chambers USA, Legal 500, the National Law Journal, Benchmark Litigation and Best Lawyers. Washingtonian magazine included Peter on its 2019 list of Washington’s Best Lawyers as one of the region’s “best legal minds” for his Supreme Court practice. Legal 500 also recognizes Peter for his work in the area of media, technology and telecommunications. Peter was recognized in the 2020 edition of Benchmark Litigation for his appellate practice, and has been since 2011. Peter is also included in the 2019 “Best Lawyers in America” directory, and has been recognized since 2011 for his appellate, commercial litigation and media law work. Peter was named Best Lawyers’ “2016 Washington DC Appellate Practice ‘Lawyer of the Year.’” In 2012, the National Law Journal/Legal Times named Peter to its list of “Champions & Visionaries,” a select group of “attorneys whose business foresight or legal acumen has expanded their firms, advanced the law or improved government.” The NLJ noted that Peter “has been front and center in almost every major energy lawsuit in the past two years.” Law360 named Peter one of its “MVPs” for Appellate Law (2014) and Energy Law (2011). 

Peter started his career at Sidley as an associate in 1989 after completing a clerkship for Justice Anthony Kennedy. In 2002 he joined the Department of Justice (DOJ) as the Principal Deputy Associate Attorney General. Peter spent most of his more than five-year tenure at DOJ as the Assistant Attorney General for the Civil Division, and ultimately served as Acting Attorney General of the United States. He returned to Sidley in 2008.


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