Mark is a 1982 graduate of Southwestern University School of Law, where he was a member of the Law Review and graduated cum laude. He spent the first few years of his career as a Deputy District Attorney for the County of Los Angeles. There, he had the opportunity to serve as lead counsel in excess of seventy jury trials and numerous bench trials.

Mark's career shifted emphasis when he moved to civil practice and, ultimately, became a senior associate in the national law firm of Arter and Hadden. There Mark's litigation experience led to his representation of large entities involved in the transportation, telecommunications and entertainment industries in civil litigation matters.  It was there, in early 1988, that he was introduced to workers' compensation, California style.

In late 1982 Mark moved to Chernow and Lieb, house counsel for Zenith Insurance Company where he served as a Senior Trial Attorney and acted as the dedicated counsel for Zenith's Special Investigations Unit.  Mark's expertise in ferreting out suspected claims contributed to the widely recognized success of that unit.

Mark and Gordon worked together at the Law Offices of George Theofanis for a number of years and opened the doors of Harrison and Geiger, LLP in March of 2003. Mark is a Certified Specialist in California Workers' Compensation Law.