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Thomas B. Mason

Thomas B. Mason

Harris, Wiltshire & Grannis LLP

Washington, DC, USA

Thomas B. Mason is the Chair of Harris, Wiltshire & Grannis LLP’s Legal Ethics and Malpractice Group. He represents lawyers and law firms in malpractice, disqualification, disciplinary investigations and prosecutions, partner admissions and departures, and law firm dissolutions. Mr. Mason’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 of the above areas so as to avoid problems or disputes before they arise. Mr. Mason was named Washington, D.C., Ethics and Responsibility Lawyer of the Year in 2014 by Best Lawyers. He has served as an expert in ethics and related issues on numerous occasions.

Some of his most notable representations include:

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.

Secured a dismissal of malpractice claims against an Amlaw 100 law firm in a multi-defendant action. The claims against the other defendants remain pending.

Handled dozens of disciplinary complaints and disqualification controversies, obtaining many outright dismissals of the former and frequently dissuading opposing counsel from even filing motions to disqualify with respect to the latter.

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 the trial level. Obtained a dismissal of all counts at the motion to dismiss state on behalf of a client based on ripeness and damages issues.

Obtained dismissals in five separate bar disciplinary matters in which the presiding judge or court filed a complaint or found misconduct against our client. Also obtained a dismissal in a bar matter in which a court had previously disqualified the client for a conflict of interest.


Prior to private practice, Mr. Mason 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 District of Columbia Public Defender Service where he had an intensive criminal trial and appellate practice.

Mr. Mason served on the D.C. Bar Legal Ethics Committee from 2006 to 2012, including three terms as Chair from 2009 to 2012. Mr. Mason is currently a member of the District of Columbia Bar Rules of Professional Conduct Review Committee. He also served on this Committee from 2002 through 2008. 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 themselves in 1991.

Mr. Mason speaks and writes frequently on ethics and malpractice matters. He is a frequent speaker at the D.C. Bar and has also spoken before various sections of the American Bar Association, the Practising Law Institute, the America Law Institute and a number of other bar and industry organizations. He has written on such topics as non-lawyer partners and multiple “of counsel” relationships with different law firms. Mr. Mason has taught ethics and professional responsibility at the Georgetown University School of Law since 2008 and has taught on various subjects at the National Institute of Trial Advocacy, Columbus School of Law at Catholic University and American University’s Washington College of Law.

Mr. Mason has been nationally recognized by Best Lawyers and Super Lawyers and he is AV Peer Review rated by Martindale-Hubbell with a 5.0 out of 5.0 rating.


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