Print PDF

Leading Antitrust Lawyer Ann O’Brien Joins Sheppard Mullin in Washington, D.C.

Former High-Ranking Woman in DOJ Antitrust Division Will Co-Lead Global Antitrust & Competition Practice

WASHINGTON, D.C., February 7, 2023 —  Sheppard, Mullin, Richter & Hampton LLP is pleased to announce that Ann M. O’Brien has joined the firm as a partner and co-leader of the Antitrust & Competition practice group. She will also lead the firm’s Criminal Antitrust and Cartels team. Based in Washington, D.C. O’Brien was most recently the leader of the Cartel and Government Antitrust Investigations Task Force at BakerHostetler.

O’Brien advises clients facing criminal and civil government antitrust investigations or litigation. She has extensive knowledge of antitrust enforcement practices and policy decisions, gained from her time working for nearly 20 years at the U.S. Department of Justice (DOJ) in the Antitrust Division and as a Special Assistant United States Attorney in the District of Maryland. Over her tenure, she served in numerous senior leadership and management positions at the Antitrust Division, notably as the Assistant Chief of two sections and as the Acting Director of Criminal Enforcement. As acting director, O’Brien was the second-highest career official and highest ranking woman running the Antitrust Division’s criminal program, where she supervised more than 120 attorneys across five offices. During her two-decade DOJ tenure, O’Brien was involved in virtually every major criminal enforcement and policy decision made by the Antitrust Division. 

“Ann is a well-known, trusted advisor whose DOJ training and compliance counseling will help our clients deter or quickly detect antitrust exposure, informed by what is most important to the Antitrust Division and the courts,” said Luca Salvi, chair of Sheppard Mullin. “In addition to her client work, Ann’s proven ability to lead large teams both at the DOJ and in private practice to successful outcomes and mentor antitrust attorneys early in their careers to blaze a path forward makes her an ideal fit for our culture and our firm.” 

Sheppard Mullin’s Antitrust & Competition practice group co-leader Leo Caseria added, “Ann’s insight on antitrust agency priorities, goals and policies is invaluable to companies facing international and multi-agency exposure. She has substantial experience leading every aspect of domestic and international antitrust and white collar investigations and prosecutions, including litigating federal criminal jury trials. I look forward to working closely with her to lead our global practice.”

Commenting on joining the firm, O’Brien said, “I am excited to join this fantastic practice at Sheppard Mullin where my leadership experience at the DOJ’s Antitrust Division and in private practice will help the firm’s clients navigate today’s intense governmental scrutiny in the U.S. and overseas.”

“I am passionate about supporting other women and promoting increased diversity in antitrust law, so I am looking forward to joining a growing antitrust team of diverse lawyers and helping to lead and mentor the next generation,” she added. 

O’Brien is regarded as a leading authority in antitrust law and was recently named to Global Competition Review’s “Women in Antitrust 2021” list, which honored an elite group of women lawyers around the world for their accomplishments in the antitrust field. O’Brien received her J.D. from Northeastern University School of Law and her B.A. from the University of Notre Dame. She also clerked for Judge Deborah Robinson of the U.S. District Court for the District of Columbia.

About Sheppard Mullin’s Antitrust & Competition Practice Group
Sheppard Mullin’s Antitrust & Competition practice is composed of more than 40 lawyers based in Washington D.C., California, Brussels, London, Seoul and Shanghai who are entirely focused on practicing antitrust and competition law. The team includes former high-ranking officials and trial lawyers from the U.S. Department of Justice, U.S. Federal Trade Commission, and the European Commission’s Directorate General for Competition, all working together, seamlessly handling matters on behalf of a diverse array of clients throughout the United States, Europe and Asia. Our practice is known for litigating some of the largest and most complex antitrust cases in the U.S., from federal multi-district class actions to civil litigation between competitors, suppliers and purchasers. We also navigate the merger review and approval process around the globe. Cartel defense work has been a pillar of our practice for decades. We were at the forefront of the explosion in international cartel cases beginning in the 1990s and have remained a leading cartel practice ever since.

About Sheppard, Mullin, Richter & Hampton LLP
Sheppard Mullin is a full-service AmLaw 100 firm with more than 1,000 attorneys in 16 offices located in the United States, Europe and Asia. Since 1927, industry-leading companies have turned to Sheppard Mullin to handle corporate and technology matters, high-stakes litigation and complex financial transactions. In the U.S., the firm's clients include nearly half of the Fortune 100. For more information, please visit


Practice Areas

Jump to Page

By scrolling this page, clicking a link or continuing to browse our website, you consent to our use of cookies as described in our Cookie and Advertising Policy. If you do not wish to accept cookies from our website, or would like to stop cookies being stored on your device in the future, you can find out more and adjust your preferences here.