Overview
Mario Nguyen is a skilled litigator, independent investigator, and trusted legal adviser with a technology-forward approach. Drawing from his experience on all sides of the courtroom—as a federal prosecutor, a criminal defense lawyer, and a law clerk to a federal judge—Mario represents governmental bodies, multinational corporations, publicly traded companies, start-ups, nonprofit organizations, celebrities, and corporate executives in complex criminal and civil litigation, internal and government investigations, administrative regulatory proceedings, and compliance counseling.
Mario built the foundation for his practice working for a former US Attorney in a major international law firm, where he tried a first-of-its-kind multi-defendant federal criminal healthcare fraud case under the Travel Act. He later joined the Fraud Section of the DOJ's Criminal Division as a Trial Attorney, where he worked on some of the most complex fraud investigations and prosecutions across the nation, including work with Task Force KleptoCapture, a multi-agency initiative enforcing economic sanctions and export controls imposed in response to Russia’s invasion of Ukraine. Mario was also a member of the Criminal Division’s Technology Committee and served as a unit liaison to the Computer Crime and Intellectual Property Section (CCIPS). Mario further honed his litigation strategy by serving as an inaugural law clerk to a newly appointed federal trial court judge in California’s Southern District, which encompasses the second most populous county in the state.
Mario draws from his experience on all sides of the courtroom to assist clients in building compliance programs; assessing and managing regulatory risks; conducting cross-border internal investigations; navigating government investigations; responding to subpoenas and search warrants; and litigating complex criminal, civil, and regulatory matters before federal and state courts, grand juries, special litigation committees, and administrative agencies. Mario is particularly adept in cross-border matters involving Latin America, given his Spanish fluency and cultural competence developed as a US Fulbright Scholar to Mexico.
Mario's technology-driven approach to the law notably elevates his legal practice. Having achieved designation as a Certified E-Discovery Specialist (CEDS), Mario is especially skilled at managing the preservation, collection, extraction, processing, analysis, review, production, and governance of extraordinarily large, complex, or cross-border datasets.
- California
- Texas
- Certified E-Discovery Specialist, ACEDS (2019)
- US District Court, Central District of California
- US District Court, Northern District of Texas
- US District Court, Eastern District of Texas
- US District Court, Western District of Texas
- Hon. Robert S. Huie, US District Court, Southern District of California
-
J.D., Harvard Law School, 2017, Harvard Legal Aid Bureau; Technical Editor, Harvard Law Journal on Legislation
- Instituto Tecnológico Autónomo de México, 2013
- B.A., Western Kentucky University, 2012, magna cum laude, Public Relations
Areas of Work
Representative Matters
White-Collar/Criminal Defense
- Defended prosecutor in appeal to state supreme court of criminal charges under California’s Anti-Hacking Statute, resulting in dismissal of all charges.
- Represented governmental body with over 3,000 employees and an annual budget of over $200 billion in federal criminal grand jury investigation into suspected multi-million dollar fraud.
- Represented surgeon in a months-long multi-defendant criminal healthcare fraud trial against first-of-their-kind federal charges under the Travel Act alleging over half a billion dollars in fraudulent billing.
- Defended healthcare marketing professional in a federal criminal grand jury investigation into suspected violations of the Anti-Kickback Statute, resulting in no criminal charges filed against the marketing professional.
- Represented celebrity and sexual assault survivor in their allegations against Harvey Weinstein.
- Defended securities trader in parallel criminal and civil securities fraud cases brought by the DOJ and SEC, alleging over $16 million in fraud.
- Represented one of the largest multinational spirits distribution companies in an investigation led by a state alcoholic beverage regulatory agency, resulting in no charges filed.
- Defended a publicly traded manufacturer in federal criminal antitrust investigation, resulting in no charges filed.
- Represented law firm in federal criminal investigation into tax fraud, resulting in no charges filed.
- Represented semiconductor engineer at publicly traded company in investigation by the DOJ and Dept. of Commerce of suspected export/import control violations related to China. No charges were filed against the engineer.
- Obtained diversion of felony criminal drug charge.
- Represented defendants against capital murder charges as a volunteer attorney for the Dallas County Public Defender’s Office in Texas.
Investigations
- Conducted internal investigation of a global non-profit organization which uncovered multimillion-dollar fraud and resulted in federal wire fraud criminal charges against the CEO.
- Appointed by special committee of select branch of the federal government to conduct internal investigation into governmental body for alleged misconduct.
- Served on investigative counsel team for a large public school district with over 200 schools and an annual budget of over $2 billion.
- Conducted internal investigation on behalf of a startup’s special litigation committee in response to shareholder derivative lawsuit alleging over $22 million of losses due to company mismanagement and breaches of fiduciary duties.
- Investigated violations of economic sanctions and export controls imposed in response to Russia’s invasion of Ukraine as part of the DOJ’s multi-agency Task Force KleptoCapture.
Commercial/Civil Litigation
- Obtained favorable settlement for dental practice holdings company with 200 offices across nine states against a qui tam whistleblower case alleging $150 million in Medicaid fraud.
- Defended celebrity against certification of federal cryptocurrency class action across 46 states, successfully limiting class to only four states.
- Obtained dismissal of a federal Racketeer Influenced and Corrupt Organizations Act (RICO) and antitrust lawsuit against an energy business consultant and related foreign companies, alleging $470 million in losses due to an $11 billion multinational government bribery scheme.
- Represented medical device start-up founder and scientist against federal civil fraud lawsuit.
- Defended Chief Technology Officer against federal qui tam whistleblower and False Claims Act lawsuit alleging $8 million in healthcare fraud.
- Obtained favorable settlement for infusion company in multi-party dispute, avoiding litigation entirely.
- Defended energy company valued at over $150 million against shareholder derivative class action.
- Obtained favorable settlement for hospitality holdings company valued at over $20 million in civil fraud lawsuit.
Compliance
- Advised sporting organization on compliance with financial reporting requirements of alcohol distribution regulations.
- Developed compliance program for multi-office specialty healthcare provider practice.
- Guided infusion nursing company on compliance with healthcare and privacy regulations.
- Advised waste management company on compliance with antitrust laws and regulations.
News & Publications
Press Releases
Steptoe Adds Former DOJ Prosecutor Mario Nguyen to Strengthen AI-Driven Investigations Practice
June 1, 2026
Noteworthy
- Best Lawyers, Ones To Watch, Criminal Defense: White Collar (2026)
- D Magazine
- Best Lawyers Under 40 (2021)
- Best White-Collar Criminal Defense Attorneys (2020)
- Dallas Association of Young Lawyers
- One-to-Watch (2020)
- Best Advocate, Trial Skills Competition (2018-2020)
- HuffPost, 40 Under 40: Latinos in Foreign Policy (2016)
- US Fulbright Scholar (2013)
Previous Employment
- Trial Attorney, Fraud Section, Criminal Division, US Dept. of Justice (2021-2022)
- Adjunct Professor, Texas A&M School of Law (2020-2026)
Professional Affiliations
- Fellow, Leadership Academy, San Diego County Bar Association (2023)
- Participant, Diverse Lawyers Trial Academy, American Bar Association (2022)
- Associate, Higginbotham Inn of Court (2020-2021)
- Leadership Class, Dallas Association of Young Lawyers (2019)
- Alumni Ambassador, US Fulbright Program (2014-present)