Marguerite M. Sullivan

  • Partner
  • 555 Eleventh Street, NW
  • Suite 1000
  • Washington, D.C. 20004-1304
  • USA
  • T +1.202.637.1027


Maggy Sullivan is a partner in the Litigation & Trial Department of Latham & Watkins and is a member of the firm’s Antitrust & Competition Practice. She is a former member of the firm’s Finance Committee and Strategic Client Committee. She has extensive experience in both private and government antitrust matters, and has defended corporate clients in cartel investigations, complex civil actions, multi-district actions, and class actions.

Ms. Sullivan focuses on antitrust class actions and business to business litigation in state and federal courts, criminal cartel investigations, and antitrust compliance counseling. She has been involved in some of the largest and most complex antitrust matters to date.

Ms. Sullivan’s antitrust work has covered a wide range of industries, including energy, consumer products, healthcare, automotive, software and technology, construction materials, specialty chemicals, textiles, medical dictation, paper, cable, and satellite.    

Ms. Sullivan received Global Competition Review’s 2017 award for Cartel Defense Civil Litigation of the Year for her work resolving multiple class action claims against global auto parts suppliers. She is recommended for her cartel defense practice by Legal 500 US. Ms. Sullivan spent two years practicing in Brussels where she was listed in Chambers 2016 and 2017 as one of the leading antitrust and competition lawyers in Brussels and recognized for her private antitrust litigation expertise and her extensive experience acting before the US Department of Justice. Ms. Sullivan is also named as a Benchmark Litigation 2018 Future Star and is featured on the Who’s Who Legal: Future Leaders 2017 – Competition list. In 2012, Ms. Sullivan was recognized as a Rising Star in Litigation at Euromoney’s inaugural America's Women in Business Law awards.

Thought Leadership

A selection of Ms. Sullivan's publications includes:

  • “US DOJ Weighs Reform Options for Antitrust Leniency Law Set to Expire,” Client Alert, April 2019 
  • “Ninth Circuit Nixes Immediate Appeals of Denials of State Action Immunity,” Client Alert, June 2017
  • “Class Action Defendants Likely to Benefit if House Bill Becomes Law,” Client Alert, March 2017
  • “Your Stipulated Protective Order May Not Provide As Much Protection As You Expect,” Client Alert, October 2016
  • “Class/Collective Actions in Europe: Overview of Applicable EU Law Principles”; chapter within the book “Class Actions – A Global Guide from Practical Law,” 2015
  • “Resale Pricing Issues,” Antitrust Law and Economics of Production Distribution, ABA Antitrust Section, 2013
  • “Three Years After Credit Suisse v. Billing: Courts Still Find The Implied Immunity Doctrine Plainly Repugnant,” Antitrust Practitioner, Vol. 7, October 2010
  • “Breaking New Ground: Direct Settlement of EC Cartel Cases,” Global Competition Review, 2008

Her recent speaking engagements include:

  • “‘Oh no! We got nailed’ – Compliance after the worst case scenario,” GCR Live 8th Annual Antitrust Law Leaders Forum, Miami, FL, February 2019
  • “Developments in Cartel Enforcement in Asia and Beyond,” ABA’s Antitrust in Asia Conference, Seoul, Korea, June 2018
  • “Managing Global Litigation,” GCR Live 3rd Annual Antitrust Litigation USA, NY, June 2017
  • “Proposed Changes to the Canadian Immunity and Leniency Programs,” BLG’s Competition/Antitrust Developments Conference, Toronto, Canada, September 2017
  • ABA Fall Forum Panel on Litigating State Regulation of Disruptive Technologies, Washington, D.C., November 2016
  • Private Antitrust Litigation: Europe vs. United States – A Comparative Discussion Providing Practical Advice for A Successful Global Defense Strategy, Latham & Watkins Seminar, Tokyo, Japan, March, 2016


Ms. Sullivan’s successes include:

  • Obtaining amnesty for a major industrial client in multiple jurisdictions around the world
  • Obtaining the first ever global resolution of criminal and civil claims (including antitrust and False Claims Act claims) asserted by the US Government on favorable terms and in record time
  • Obtaining dismissal of a monopolization claims against a natural gas and energy supplier based on the Filed Rate Doctrine and lack of antitrust standing
  • Obtaining dismissal of boycott claims against a table saw manufacturer based on insufficient allegations of conspiracy
  • Obtaining dismissal of price fixing claims against a Japanese auto parts supplier on jurisdictional grounds

She currently represents a generic pharmaceutical manufacturer and multiple auto parts manufacturers in the two largest and most complicated multi-district class action litigations ever filed.

Examples of other multidistrict class actions include:

  • In re Inductors Antitrust Litigation
  • In re Aftermarket Filters Antitrust Litigation
  • In re Baby Products Antitrust Litigation
  • In re Pressure Sensitive Labelstock Antitrust Litigation
  • In re Polyester Staple Antitrust Litigation

Thought Leadership

  • Key Aspects Of DOJ's Government Procurement Antitrust Initiative -  November 21, 2019
  • New DOJ Guidance Increases Benefits for Robust Antitrust Compliance Programs — What Companies Need to Know -  July 15, 2019
  • US DOJ Weighs Reform Options for Antitrust Leniency Law Set to Expire -  April 16, 2019
  • Ninth Circuit Nixes Immediate Appeals of Denials of State Action Immunity -  June 15, 2017
  • Class Action Defendants Likely to Benefit if House Bill Becomes Law -  March 15, 2017
  • Your Stipulated Protective Order May Not Provide As Much Protection As You Expect -  October 20, 2016
  • Class Actions - Overview of Applicable EU Law Principles -  October 05, 2015
  • Proposed Cartel Enforcement Regulations in Brazil -  January 23, 2013
  • EU Cartel Enforcement—Proposed New Settlement Procedures -  November 16, 2007
  • Breaking New Ground: Direct Settlement of EC Cartel Cases -  September 01, 2007
  • Second Circuit Finds State Common Law Claims Involving FDA Premarket Approved Medical Devices Preempted -  July 18, 2006

"She is one of the reasons we hold the firm in such high regard."  

“An excellent lawyer, providing very logical advice. I trust anything she says."

Chambers Global 2016-2017
Bar Qualification
  • District of Columbia
  • Virginia
  • JD, Northwestern University School of Law, 2000
  • BA, Bowdoin College, 1995
  • Automotive
  • Energy & Infrastructure
  • Retail & Consumer Products
  • Antitrust & Competition
  • Litigation & Trial Practice
  • Complex Commercial Litigation