Thomas B. Mason



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’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. Tom was named Washington, D.C., Ethics and Professional Responsibility Lawyer of the Year for 2014, 2017, 2019, and Legal Malpractice Law – Defendants Lawyer of the Year for 2018 and 2022 by Best Lawyers. He was also selected to Excellence in Practice for seven years by Super 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.
  • 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.
  • Regularly represents the District of Columbia Public Defender Service, the Legal Aid Society of the District of Columbia, Bread for the City, and other legal service organizations and their lawyers on a pro bono basis.

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 District of Columbia Public Defender Service where he had an intensive criminal trial and appellate practice.

Tom is a member of the D.C. Bar’s Global Legal Practice Committee and a past member of the American Bar Association’s Standing Committee on Ethics and Professional Responsibility. 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 also served on the D.C. Bar Rules of Professional Conduct Review Committee from 2002 to 2008 and then again 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 frequent 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. He has written on topics such 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 from 2008 to 2016 and has taught various subjects at the National Institute of Trial Advocacy, Columbus School of Law at Catholic University and American University’s Washington College of Law.

He is AV Peer Review rated by Martindale-Hubbell with a 5.0 out of 5.0 rating, High Ethical Standing and Highest Level of Professional Excellence.


Columbia Law School, J.D.

Yale University, B.A., cum laude


Hon. Frank Kaufman, U.S. District Court for the District of Maryland



At HWG, we’re always looking for smart, talented people to add to our team.


  • 1919 M Street NW, Eighth Floor
    Washington, DC 20036-3537
  • 333 Fayetteville Street, Suite 1500
    Raleigh, NC 27601