31 Aug 2026
Sullivan & Cromwell Welcomes Sonia Kuester Pfaffenroth as Partner in Antitrust Group
"Sullivan & Cromwell has hired former DOJ Deputy Assistant Attorney General Sonia Kuester Pfaffenroth as a partner in its Antitrust Group in Washington, D.C., to work on antitrust litigation, investigations and counseling."
Ms. Pfaffenroth’s practice encompasses federal and state antitrust litigation and investigations, as well as compliance, training and strategic counseling across a broad range of competition issues, including pricing, marketing, distribution, contracting, trade associations, research and development collaborations. She counsels on international cartel investigations, merger and acquisition reviews and civil antitrust litigation. She joins Sullivan & Cromwell at the partner level.
Ms. Pfaffenroth brings extensive government experience from the Antitrust Division of the U.S. Department of Justice, where she served as Deputy Assistant Attorney General for Civil and Criminal Operations and as Deputy Assistant Attorney General for Civil Enforcement. In those roles she oversaw both civil and criminal enforcement efforts, the Division’s work with competition law enforcement agencies worldwide, legal policy initiatives and competition advocacy, and supervised significant matters including litigation challenging the Anthem/Cigna and Aetna/Humana mergers.
Ms. Pfaffenroth earned her J.D. from Stanford Law School, Order of the Coif, and her B.A. from Carleton College, magna cum laude, and clerked for Judge Paul Friedman of the U.S. District Court for the District of Columbia.