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Member Directory

Thomas O'Brien

Ellis George LLP - Los Angeles
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Thomas O'Brien
Ellis George LLP - Los Angeles
Los Angeles,

Thomas P. O’Brien, a Partner with Ellis George Cipollone O’Brien Annaguey LLP, was formerly a partner at an international law firm for nearly a decade, where he led the firm’s west coast white-collar litigation practice and served as chair of the Los Angeles Litigation Department. Prior to joining private practice, Mr. O’Brien served as the United States Attorney for the Central District of California, having been appointed by President George W. Bush and unanimously confirmed by the United States Senate. Mr. O’Brien represents corporations and individuals in all phases of government investigations and prosecutions, including cases under federal and state False Claims Act statutes (also known as qui tam matters) and the Foreign Corrupt Practices Act, health care fraud issues, and other corporate compliance matters, guiding his clients from their first contact with government authorities all the way through trial. He also regularly conducts internal investigations for corporations and municipal governments into potential violations of law or other wrongdoing, and advises clients on complex white-collar matters such as embezzlement, accounting fraud, bribery, and other issues.

Mr. O’Brien is a nationally recognized trial attorney. He is a U.S. Fellow with the International Academy of Trial Lawyers, an honor limited to 500 trial attorneys in the United States; a member of the National Trial Lawyers: Top 100; and has been noted by Chambers USA for his “fantastic instincts and courtroom skill.” Mr. O’Brien has successfully tried over 100 criminal and civil cases in federal and state courts throughout the nation. He has represented national and multi­national companies in civil actions with billions of dollars in dispute, and has successfully represented individual corporate leaders and foreign heads of state in civil, criminal, and regulatory proceedings. He has unparalleled experience navigating dual civil-criminal proceedings and handling complex, first-of-its-kind matters in multiple jurisdictions, including matters conducted in foreign nations.

During his tenure as United States Attorney, Mr. O’Brien had responsibility over all federal criminal and tax investigations and prosecutions as well as all civil matters involving the United States in the largest federal district in the country. Under his leadership, the office filed the most felony cases in the history of the district and increased complex case filings by 50 percent. The office also filed the largest gang RICO case in the history of the Department of Justice, the largest RICO case against a motorcycle gang and, for the first time in the nation, seized the gang’s trademark. The office also filed the largest tax restitution case in IRS history. Mr. O’Brien served on the President’s Corporate Fraud Task Force and was a member of the Attorney General’s Advisory Committee’s Cyber/Intellectual Property Subcommittee.

Before he was confirmed as United States Attorney, Mr. O’Brien served for more than two years as Chief of the Criminal Division. In that capacity, he oversaw several high-profile espionage cases, helped bring the first treason case in the nation since World War II, supervised several high-profile public corruption and civil rights cases, brought charges under several cyber-crime statutes for the first time in the nation, and oversaw some of the largest fraud cases in the United States. He was the only Criminal Chief in many years who tried cases during his tenure.

Prior to serving as Criminal Chief, he was an Assistant United States Attorney for four years before rising to Chief of the Civil Rights Section, where he personally investigated and prosecuted numerous matters, including federal hate crimes, human trafficking violations, and police misconduct cases. Before becoming a federal prosecutor, Mr. O’Brien was a Deputy District Attorney in Los Angeles County assigned to the Hardcore Gang Division, where he tried 35 gang murder cases.

Upon graduation from the United States Naval Academy, Mr. O’Brien accumulated over 2,000 flight hours as a Radar Intercept Officer in the F-14A Tomcat fighter with the United States Navy and served on two overseas deployments on active duty. He is a graduate of the United States Navy Fighter Weapons School commonly known as TOPGUN.

Recent Representations

  • Led the successful defense of a medical doctor charged in a $355 million federal health care fraud prosecution. After a three-month trial, the jury fully acquitted Mr. O’Brien’s client on all 33 felony counts. All other defendants were convicted on all counts.
  • Led the successful defense of a U.S. Navy admiral in connection with the federal “Fat Leonard” bribery prosecution. After a four-month trial, the jury could not reach a verdict on any count against Mr. O’Brien’s client. The jury convicted all other defendants on all counts.
  • Led the successful defense of an individual charged in the nation’s first-ever federal “birth tourism” prosecution. Mr. O’Brien negotiated a plea agreement where his client pleaded guilty to only two counts of a 28-count indictment. Despite the government seeking a sentence of 33 months imprisonment, Mr. O’Brien secured a sentence of time-served and minimal supervised release. Mr. O’Brien also recovered for the client several million dollars-worth of assets that had initially been seized by the government in connection with this prosecution.
  • Represented an individual investigated by the Department of Justice for allegedly participating in an insider trading scheme. Mr. O’Brien persuaded the DOJ not to indict his client, even though the DOJ indicted and secured convictions against several other individuals allegedly associated with the scheme.
  • Represented an individual in connection with one of the nation’s first-ever criminal investigations and charges under the Foreign Agents Registration Act (FARA).
  • Obtained a multi-million-dollar pre-litigation settlement on behalf of a client alleging sexual assault.
  • Secured a successful settlement on behalf of the former chief executive officer of a commercial cannabis company who was wrongfully terminated.
  • Represented a hospital in connection with an investigation by the Department of Justice and Office of the Inspector General into potential violations of the False Claims Act and federal Anti-Kickback Statute.
  • Successfully led the defense of a university professor in a high-profile felony prosecution involving alleged labor code violations, which resulted in the charges being dismissed. The case garnered national media attention in what has been described as the first case of its kind.
  • Represented a major national services corporation in a Department of Justice investigation concerning allegations that the company violated the False Claims Act. The investigation was closed by the Department of Justice with no charges being brought.
  • Led a team to effectively defend a local government entity during a two-year DOJ investigation into allegations of corruption in a billion dollar purchasing project.
  • Represented a foreign conglomerate in a high-profile criminal matter involving allegations of international trade secret theft in the Eastern District of Virginia.
  • Spearheaded the internal investigation into serious allegations of fraud against a medical device manufacturer. At the conclusion of the investigation, Mr. O’Brien’s team made a multi-hour presentation to the government resulting in the termination of the investigation into the client.
  • Assisted in representing a former CEO against allegations that the client engaged in insider trading in connection with a secondary offering. The client was acquitted on all charges at trial.
  • Pioneered a novel settlement strategy for a medical device manufacturer to resolve criminal allegations brought against it in connection with alleged Cal/OSHA violations.
  • Led a federal trial team to a front-page defense victory for a sheriff’s deputy accused of obstruction of justice, where the jury was unable to reach a verdict on the counts charged.
  • Successfully led a team of attorneys in conducting an internal investigation at the request of a Southern California health center. That investigation, since closed, arose out of allegations that employees of the health center accepted improper benefits in exchange for referrals to certain patient facilities in violation of federal and state anti-kickback statutes.
  • Persuaded the Department of Justice not to file fraudulent billing charges against a physician with a successful medical practice. When Mr. O’Brien was brought onto the case, the investigation had been ongoing for several years, and the government had issued a final plea offer and expressed their intention to indict the client. Within weeks, Mr. O’Brien and his team conducted an investigation and presented new evidence to the Department of Justice. The Department of Justice decided to allow the statute of limitations to expire on the charges that they, only weeks earlier, had intended to file.
  • Successfully represented the police chief of a local city who faced civil charges filed by the state Attorney General as part of allegations against an entire city council and several administrators for defrauding taxpayers and wasting taxpayer monies. In a case described by numerous media outlets as one of the biggest corruption cases in the nation, and despite the extreme public outcry attacking his client, Mr. O’Brien and his team convinced the court to dismiss the complaint with prejudice.
  • Represented a local airport commission in an investigation by the Federal Bureau of Investigation into allegations of corruption. Within months of being retained in this case, Mr. O’Brien managed to focus the government on the actions of other individuals and received a letter from the Department of Justice clearing his client.

Practice Areas

  • White-Collar Criminal and Regulatory Defense
  • Investigations
  • Complex Litigation
  • Class Actions

Accolades and Recognitions

  • Los Angeles Business Journal: “Leaders of Influence: Litigators & Trial Attorneys,” 2022
  • Chambers USA, Litigation: White-Collar Crime & Government Investigations
  • Los Angeles Times: “Business of Law: Trends, Updates, Visionaries,” Legal Visionaries, 2022
  • U.S. Fellow: International Academy of Trial Lawyers (by invitation)
  • National Trial Lawyers: Top 100 (by invitation)
  • 2008 Immigration and Customs Enforcement Assistant Secretary’s Award for Excellence in Law Enforcement
  • 2007 Anti-Defamation League Pacific Southwest Region’s Helene and Joseph Sherwood Prize for combating hate
  • 2007 Attorney General’s Award for Exceptional Service, the highest award given by the Attorney General, for his role in investigating and prosecuting street gang members who committed hate-crime murders of African Americans in Northeast Los Angeles
  • 2000 Deputy District Attorney of the Month Award for successfully prosecuting two back-to-back gang murder cases in the month of July
  • Received awards from many different organizations, including the Los Angeles City Council; Los Angeles Police Department; Federal Bureau of Investigation; Drug Enforcement Administration; United States Secret Service; Internal Revenue Service; United States Marshal’s Office; Santa Barbara District Attorney’s Office; United States Postal Service; United States Postal Inspectors and Office of Inspector General; Bureau of Alcohol, Tobacco, Firearms and Explosives; and the Los Angeles City Attorney

Professional and Community Involvement

  • Vice-Chair, ABA Section of International Law, International Anti-Corruption Committee, Steering Committee, Asia Regional Forum
  • Member, Legal Advisory Committee for the Anti-Defamation League
  • Former Board Member, Chandler School in Pasadena, California
  • Former Chair, Attorney General’s Advisory Committee’s Cyber/Intellectual Property Subcommittee
  • Former Board Member, Legal Aid Foundation of Los Angeles (LAFLA)


  • University of San Diego School of Law, J.D., cum laude, 1993
  • Associate Editor of the San Diego Law Review
  • United States Naval Academy, B.S., 1981

Bar Admissions

  • California

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