Ann M. O'Brien


Washington, D.C.
T +1.202.861.1650
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Ann O'Brien is the leader of the Cartel and Government Antitrust Investigations Task Force at BakerHostetler, which was formed to advise clients facing criminal or civil government antitrust investigations or litigation. Ann’s insight on antitrust agency priorities, goals and policies are a valuable asset 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. Additionally, she provides clients with cutting-edge compliance counseling and training that can help deter or quickly detect antitrust exposure, informed by what is most important to the Antitrust Division and the courts.

Ann also serves as an antitrust and white collar resource to BakerHostetler's Digital Transformation and Data Economy team, providing clients with strategic counsel on the intersection of antitrust and data ownership and privacy. She was recently named to Global Competition Review’s “Women in Antitrust 2021” list, which recognizes 138 women around the world for their accomplishments in the antitrust field.  

Ann has extensive knowledge of antitrust enforcement practices and policy decisions, gained from her time working at the U.S. Department of Justice in the Antitrust Division and as a Special Assistant United States Attorney in the District of Maryland. During her nearly 20-year tenure, she assumed numerous senior leadership and management positions in the Antitrust Division, notably as the Assistant Chief of two sections and as the Acting Director of Criminal Enforcement. She was involved in virtually every major criminal enforcement and policy decision made by the Antitrust Division for nearly two decades, and reviewed and approved hundreds of case recommendations, leniency recommendations, search warrants, and requests for grand jury or preliminary inquiry authority. Notably, she gained comprehensive knowledge of antitrust corporate compliance and developed strong relationships with domestic and foreign antitrust enforcers and regulators. Additionally, Ann served as the Antitrust Division representative on the Financial Fraud Enforcement Task Force, as well as a member of the Grant Fraud Working Group and Oil and Gas Price Fraud Working Group.

Having established herself as a thought leader in the antitrust community, Ann regularly speaks and writes on a broad-range of antitrust topics. She has also trained hundreds of antitrust prosecutors and law enforcement agents, and served as a liaison to other DOJ components and government agencies. Utilizing her in-depth understanding of antitrust policy and prosecution, Ann skillfully guides clients through their unique antitrust and white collar matters.

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Ann is a Non-Governmental Advisor to the International Competition Network (ICN), an international organization of more than 140 competition agencies with the common aim of addressing practical antitrust enforcement and policy issues.

Select Experience

  • Represent Fortune 500 company through Antitrust Division Leniency Policy marker process in matter presenting complex legal and factual issues.
  • Representing a corporate subject of an Antitrust Division criminal no poach investigation.
  • Representing an individual employee in an Antitrust Division criminal price-fixing investigation.

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  • Represent Fortune 500 company through Antitrust Division Leniency Policy marker process in matter presenting complex legal and factual issues.
  • Representing a corporate subject of an Antitrust Division criminal no poach investigation.
  • Representing an individual employee in an Antitrust Division criminal price-fixing investigation.
  • Providing antitrust compliance advice and training for multiple global companies.
  • Representing corporate third-party subpoena recipient in U.S. v. Google and State of Colorado et al. v. Google civil antitrust lawsuits.
  • Advise corporation on responding to government compulsory process for customer information and data, including the privacy, data protection and criminal procedure implications of responding to law enforcement requests.
  • Representing an advertising platform third-party CID recipient in Texas attorney general antitrust investigation of Google.
  • Formulated and implemented Antitrust Division criminal policy and advised Antitrust Division leadership, management, and staff on complex and high-profile criminal policy, leniency, investigative strategy, sentencing, compliance program assessment, and international issues.
  • Provided insight on antitrust compliance and the evaluation of corporate antitrust compliance programs and was a primary drafter of the Antitrust Division’s 2019 compliance guidance.
  • Counseled clients on pricing strategy for essential products and adherence with federal, state and local price gouging laws during COVID-19 pandemic.
  • Supervised antitrust policy and legislative matters. Also responded to congressional inquiries and oversight matters, briefed congressional staff on various subject matter, and drafted congressional testimony.
  • Oversaw work of five criminal offices and reviewed every type of request, including hundreds of case recommendations and scores of leniency recommendations, search warrants, and requests for immunity, grand jury, and preliminary inquiry authority.
  • Worked with the Criminal Division Fraud Section on a parallel FCPA investigation and worked to reach a first-of-its-kind corporate resolution binding both the Antitrust and Criminal Division and resulting in $579 million in criminal fines and disgorgement – the second-largest FCPA fine paid by a U.S. company at that time.
  • Represented the United States in criminal proceedings in multiple districts, including in dozens of sentencings, plea, and motions hearings in real estate foreclosure auction cases nationwide.
  • Collaborated with other domestic and international agency leaders to coordinate law enforcement efforts for international investigations affecting the U.S. and abroad, including foreign competition and enforcement agencies, U.K.’s Serious Fraud Office and Financial Conduct Authority, DG Comp, South Africa Competition Commission, and numerous competition agencies in Latin America and Asia.
  • Worked on international extraditions involving antitrust defendants and foreign assistance requests pursuant Mutual Legal Assistance Treaties (MLAT) and International Antitrust Enforcement Assistance Act (IAEAA).

Recognitions and Memberships


  • Global Competition Review’s "Women in Antitrust 2021” list, which recognizes 138 women around the world for their accomplishments in the antitrust field
  • The Legal 500 United States (2021)
    • Recommended in Litigation: Civil litigation/class actions
  • U.S. Department of Justice, Antitrust Division
    • Assistant Attorney General Award (2006, 2015)
    • Special Achievement Award (2009)
  • Counsel of the Inspectors General on Integrity and Efficiency: Award for Excellence (2013)
  • U.S. General Services Administration OIG: Special Recognition Award (2012)



Press Releases





  • CYO Youth Basketball Coach (2018)
  • Justice Department Child Development Center, Just Us Kids
    • Vice President (2016 to 2017)
    • Board Member (2015 to 2016)
  • Shrine of the Most Blessed Sacrament Parish and School
    • Giving Tree Holiday Gift Giving Program: Coordinator (2014 to 2016)
    • School Advisory Board, Strategic Planning Extracurricular Committee: Member (2015 to 2018)

Featured Video

Antitrust Enforcement in the Biden Administration: What to Expect
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Hear a discussion on what we can expect from the Biden Administration on the antitrust front.

Prior Positions

  • U.S. Department of Justice, Antitrust Division:
    • Competition Policy & Advocacy Section: Assistant Chief
    • Office of the Assistant Attorney General: Acting Director of Criminal Enforcement
    • Washington Criminal II Section: Assistant Chief
    • Office of the Assistant Attorney General: Counsel to the Assistant Attorney General (AAG)
    • Office of Criminal Enforcement: Senior Counsel to the Deputy AAG for Criminal Enforcement
    • Office of Operations: Special Assistant to the Directors of Civil and Criminal Enforcement
    • Cleveland Field Office: Trial Attorney
  • U.S. Attorney's Office, District of Maryland: Special Assistant U.S. Attorney
  • The Honorable Deborah A. Robinson, U.S. District Court for the District of Columbia: Law Clerk


  • U.S. Supreme Court
  • U.S. Court of Appeals, Fourth Circuit
  • U.S. District Court, District of Connecticut
  • U.S. District Court, District of Columbia
  • U.S. District Court, District of Maryland
  • Maryland
  • District of Columbia
  • Pennsylvania


  • J.D., Northeastern University School of Law, 1999
  • B.A., Government and International Studies, University of Notre Dame, 1996


In The Blogs

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Antitrust Advocate
DOJ Antitrust Brings First Criminal Monopolization Case in More Than 40 Years
By Lindsey Olson Collins, Carl W. Hittinger, Ann M. O'Brien
November 4, 2022
Key Takeaways U.S. v. Nathan Nephi Zito is the first criminal monopolization case in more than 40 years, reversing the Antitrust Division’s practice of pursuing monopolization cases only civilly. The elements enumerated in the Zito plea...
Antitrust Advocate
DOJ Antitrust Division Not Backing Down on Labor
By Ann M. O'Brien, Kayley B. Sullivan
September 27, 2022
Despite back-to-back losses in the Department of Justice’s (DOJ) first-ever criminal no-poach and wage-fixing cases, the Antitrust Division (the Division) is not backing down from its enforcement focus on labor. In fact, the Division and...
Antitrust Advocate
Federal Court Allows Price-Fixing Class Action to Proceed Against Universities
By Tyson Y. Herrold, Carl W. Hittinger, Ann M. O'Brien, Nicholas M. Rose
September 14, 2022
Seventeen of U.S. News & World Report’s top 25 universities in the nation recently lost their bid to dismiss allegations of an antitrust conspiracy to suppress student financial aid awards. The ruling by the U.S. District Court for the...
Antitrust Advocate
PGA Tour Wins First Round in Antitrust Legal Fight with Players
By Ann M. O'Brien, Alyse F. Stach
August 10, 2022
On August 9, 2022, a federal judge hearing the antitrust lawsuit filed by 11 professional golf players against the PGA Tour ruled against three of the players who had sought a temporary restraining order. The order, if granted, would have...
Antitrust Advocate
Is antitrust liability in the future for the PGA Tour, and beyond?
By Ann M. O'Brien, Alyse F. Stach
August 4, 2022
On August 3, 2022, 11 professional golfers, led by Phil Mickelson, filed an antitrust complaint in the Northern District of California against the PGA Tour for the actions it took against the golfers – including suspension from PGA Tour...