In 1981, Mr. O'Brian was appointed as a Judge of the Ontario High Court of Justice (now the Superior Court of Justice). He retired from the Court in 1998 to become a mediator and arbitrator.

As a Mediator and Arbitrator, Mr. O'Brian has presided over numerous complex commercial disputes, personal injury claims, insurance and reinsurance issues, coverage disputes, loss transfers, medical malpractice claims and claims against lawyers, stockbrokers, insurance agents and other professionals.

Prior to his appointment to the Bench, Mr. O'Brian was a Trial and Appellate Counsel in Civil Litigation for the law firm of Cassels Brock & Blackwell, Toronto. He is a graduate of Queen’s University, B.A., 1955; Dalhousie University, LL.B., 1958; was called to the Bar in Ontario in 1960 and received his Queen’s Counsel in 1974.

While on the Bench, Mr. O'Brian was most active in presiding over complex civil actions which involved personal injury, medical malpractice, insurance disputes, and errors & omissions claims involving lawyers, stockbrokers and other professionals. In addition, he dealt with various other commercial litigation cases.

As part of his judicial duties, Mr. O'Brian spent considerable time as a member of the Ontario Divisional Court, which dealt with Appeals from Administrative Boards and various Tribunals.

During his last two years on the Bench, Mr. O'Brian organized and administered a long trials programme for the Toronto area which dealt with complex civil actions. In addition to administering the Judges involved in that program, Mr. O'Brian presided over several of the actions himself.

In the last year and a half of his time on the Bench, Mr. O'Brian became intensely involved in settlement conference using mediation skills as a format of assisting counsel in finding a mutually agreeable resolution of disputes.

Throughout his career, Mr. O'Brian was keenly interested in legal education. He served as an instructor in the Bar Admission Course in Civil Procedure II (Trial Advocacy) for six years and as the head of that course for an additional five years.

Mr. O'Brian is a past member of Council of the Medico-Legal Society of Ontario, past Chairman of the Insurance Subsection of the Canadian Bar Association (Ontario) and a past Director and past President of The Advocates’ Society of Ontario. In addition, he participated in numerous programs for The Law Society of Upper Canada and other professional organizations as a panellist or chair of programs dealing with various aspects of civil litigation.

In his private practice, prior to his appointment to the Bench, Mr. O'Brian was engaged as counsel for defendants and plaintiffs in numerous personal injury matters and all forms of insurance and reinsurance disputes.

Mr. O'Brian received Mediation training through a program sponsored by the Ontario Government. In addition, he is an Accredited Mediator through the Harvard Mediation Program offered through The Advocates’ Society.