Karen Kazmerzak

Karen Kazmerzak is a Partner in the Firm’s Washington, D.C. office. A former lawyer within the Federal Trade Commission (FTC), Karen has extensive experience advising clients on antitrust concerns in connection with complex transactions, including obtaining merger clearance in the United States and developing strategies to advocate for antitrust approval in international jurisdictions.

Recognized as a leader in the field by Chambers USA (2018-2023) and a “Litigation Star” by Euromoney’s Benchmark Litigation (2023), Karen is lauded by clients for providing “practical-minded guidance.” She is also recognized for her work representing third-party market participants in connection with opposition to acquisitions and in connection with government subpoenas. Beyond her work for clients on merger clearance matters, she also advises on antitrust matters involving licensing, distribution, pricing and competitor collaborations.

Karen’s extensive private sector and government experience has spanned numerous sectors, including several regulated industries, such as life sciences, energy, transportation, healthcare and telecom, among many others.  

Prior to joining Simpson Thacher, Karen was co-leader of the global Antitrust/Competition practice at another international firm. She served as an attorney with the FTC from 2006 to 2010.

Karen’s representative matters prior to joining Simpson Thacher include:

• Medline Industries on antitrust clearances related to its acquisition of medical products supplier Centurion Medical Products Corporation
• Sigma-Aldrich in connection with regulatory clearances for the company’s acquisition by Merck KGaA
• Anadarko Petroleum Corporation on antitrust clearances related to its sale of certain upstream and related assets to WildHorse Resource Development Corporation
• Pandora on antitrust clearances relating to its acquisition by SiriusXM and its sale of Ticketfly to Eventbrite
• Tribune Publishing (briefly Tronc, Inc.) on antitrust clearances for the sale of an interest in the company to Merrick Media
• Bodega Latina Corporation on antitrust aspects of its acquisition of Smart & Final Holdings from funds managed by affiliates of Apollo Global Management
• Obtaining the dismissal of a federal court antitrust claim against a major standard-setting body
• Successfully defending an auto parts distributor in an investigation of its supply agreements by the FTC

Karen is an established thought leader on antitrust topics and is an active member of the American Bar Association’s Antitrust Section. She currently serves as an associate editor of Antitrust and previously served as a vice chair of the Transportation and Energy Industries Committee (2012–2018). Karen also co-founded the Women’s Antitrust Forum, a Washington, D.C.-based organization that is focused on bringing together and creating development opportunities for women practicing antitrust law, policy and economics. She also serves as Secretary on the Board of Network for Victim Recovery of DC (NVRDC), a community-based nonprofit that provides free, comprehensive advocacy, case management and legal services to crime victims.

Karen received her J.D. from the University of Iowa College of Law and her B.S. in Microbiology from the University of Iowa. She is admitted to practice in the District of Columbia and New York.