Before joining the University of Maryland faculty in 1974, Professor Gibson practiced law in Baltimore and taught at the University of Virginia School of Law. He has taught in numerous workshops for judges and has written in the area of evidence. He was reporter to the Court of Appeals of Maryland Standing Committee on Rules of Practice and Procedure and a member of the committee that drafts the Multi-State Bar Exam.

He has served as associate deputy attorney general of the United States and as a member of the Board of School Commissioners of Baltimore City. He is a member of the Governor's Commission to Revise the Annotated Code of Maryland.