Thomas B. Mason represents lawyers and law firms on professional responsibility and ethics matters, including malpractice, disqualification, disciplinary investigations and prosecutions, partner admissions and departures, and law firm dissolutions. Tom is the founding member of HWG’s Legal Ethics and Malpractice group.

Tom’s disciplinary experience includes matters before the USPTO’s Office of Enrollment and Discipline (OED) as well as numerous state bars. He also counsels and advises lawyers and law firms in all the above areas so as to avoid problems or disputes before they arise. Tom was named Washington, D.C., Ethics and Professional Responsibility Lawyer of the Year for 2014, 2017, 2019 and 2024, and Legal Malpractice Law – Defendants Lawyer of the Year for 2018 and 2023 by Best Lawyers. He has served as an expert in ethics and related issues on numerous occasions.

• On behalf of a national telecommunications carrier, obtained a dismissal at the pleading stage of a claim for nearly $10 million in outstanding legal fees purportedly due to the former outside counsel.
• Handled dozens of disciplinary complaints and disqualification controversies, obtaining many outright dismissals, and often dissuading opposing counsel from filing motions to disqualify.
• Successfully defeated a motion to disqualify brought by one AmLaw 100 firm against another AmLaw firm.
• Litigated numerous malpractice cases at both the appellate and trial level. Obtained dismissals of all counts at the motion to dismiss stage on behalf of multiple clients based on ripeness, causation, and damage issues.

Prior to private practice, Tom worked for the Federal Public Defender for the District of Maryland, where he represented clients in a wide variety of cases, including espionage, civil rights, mail and wire fraud, and controlled substance prosecutions. He went on to join the Public Defender Service for the District of Columbia, where he had an intensive criminal trial and appellate practice.

Tom is a member of the D.C. Bar Innovations in Legal Practice Committee and a past member of the American Bar Association Standing Committee on Ethics and Professional Responsibility. Tom served on the D.C. Bar Legal Ethics Committee from 2006 to 2012, including three terms as Chair from 2009 to 2012. Tom also served on the D.C. Bar Rules of Professional Conduct Review Committee from 2002 to 2008 and from 2013 to 2020, including terms as Vice-Chair and Chair. During his tenure, the Committee adopted the most extensive revisions to the D.C. Rules of Professional Conduct since the D.C. Bar adopted the Rules in 1991.

Tom speaks and writes frequently on ethics and malpractice matters. He is a regular speaker at the D.C. Bar and has also spoken before various sections of the American Bar Association, the Practising Law Institute, the American Law Institute, and a number of other bar and industry organizations. Tom consistently earns praise for the caliber of his presentations, particularly his thorough examination of nuanced topics and detailed knowledge of the subject matters he addresses. He has written on topics such as non-lawyer partners and multiple “of counsel” relationships with different law firms. Tom taught ethics and professional responsibility at Georgetown Law from 2008 to 2016 and has taught various subjects at the National Institute for Trial Advocacy, The Catholic University of America Columbus School of Law, and American University Washington College of Law.