Thomas J. Johanson is a Partner with Marks, O’Neill, O’Brien, Doherty & Kelly’s Philadelphia office.  He is admitted to practice in Pennsylvania and New Jersey.  He is also a member of the Philadelphia and Pennsylvania Bar Associations.

Tom graduated from St. Joseph’s University in 1974, with a Bachelor of Arts in Politics.  Later, he  attended Widener University, School of Law, graduating in 1978.  During law school, Tom worked full-time in the Philadelphia District Attorney’s office in various capacities including presenting homicide preliminary hearings.  Following graduation, Tom served as an Assistant District Attorney under the former governor of Pennsylvania, Edward G. Rendell, in various roles, including prosecuting some of the worst criminals in the office’s Career Criminal Unit.

Tom left the District Attorney’s office and worked in civil defense litigation defending multi-million dollar claims in product liability, toxic torts and medical negligence to over 150 jury trials.  Additionally, Tom served as a Hearing Officer for the Pennsylvania Securities Commission and as an Arbitrator for the Philadelphia Stock Exchange.

Since joining Marks O’Neill in 2006, Tom has represented clients in toxic torts, civil rights and medical malpractice. Tom has tried cases throughout, Pennsylvania, New York, Maryland and other jurisdictions.

In Tom’s free time, he enjoys golfing, sailing and biking.  He lives with his wife, Susan, in Maple Glen, Pennsylvania.

Thomas J. Johanson
Partner / Philadelphia

Phone 215-832-4219

Thomas J. Johanson PDF


  • J.D., Widener University School of Law, 1978
  • B.A., St. Joseph’s University, 1974

Bar Admissions

  • New Jersey, 1985
  • Pennsylvania, 1979
  • U.S. Court of Appeals, Third Circuit, 1979
  • U.S. District Court for the Eastern District of Pennsylvania, 1979
  • U.S. District Court of New Jersey, 1985

Bar Associations

  • Pennsylvania Bar Association
  • Philadelphia Bar Association

Practice Areas

  • Healthcare & Catastrophic & Excess Loss
  • Construction Accident/Construction Defect
  • Professional Liability
  • Toxic Tort, Mass Tort, Environmental and Products Liability

Representative Cases



One Penn Center, 1617 John F. Kennedy Blvd., Suite 1010, Philadelphia, PA. 19103