Sonia Kuester Pfaffenroth rejoined Arnold & Porter in 2017 from the Antitrust Division of the US Department of Justice (DOJ) where she served most recently as Deputy Assistant Attorney General for Civil and Criminal Operations. In that role, Ms. Pfaffenroth was responsible for supervising both civil and criminal antitrust enforcement efforts, as well as the Division's work with antitrust and competition law enforcement agencies worldwide.
While at the DOJ, Ms. Pfaffenroth oversaw a number of the Division's most significant matters, including the Division's challenges to the Anthem/Cigna and Aetna/Humana mergers and the American Express litigation. In addition to her responsibilities with respect to the Division's international program, she also supervised a broad range of legal policy initiatives and competition advocacy efforts. She previously served as Deputy Assistant Attorney General for Civil Enforcement at the Antitrust Division and Chief of Staff and Senior Counsel to former Assistant Attorney General for Antitrust Bill Baer.
Before leaving to join the DOJ in 2013, Ms. Pfaffenroth was a partner at the firm, where she represented companies in a range of industries in international cartel investigations, merger and acquisition reviews and civil antitrust litigation, as well as providing day-to-day antitrust counseling.
Ms. Pfaffenroth originally joined Arnold & Porter in 2005 after clerking for Judge Paul Friedman of the US District Court for the District of Columbia.