Prior to joining the ICTY, he served as a Federal prosecutor with the US Department of Justice in Washington D.C. and a Unity Chief for the Environmental Crime Section. He represented the state in the cases United States vs. Exxon Corporation and United States vs. Exxon Shipping Company. In recognition of that work he was awarded the second highest Department of Justice award.
He received his Juris Doctor degree in 1971 from Hastings College of the Law, University of California, and has been a member of the California Bar Association since 1972. He has instructed law students at the UN Interregional Crime and Justice Research Institute and Stanford Law School, and authored several publications on the ICTY and international criminal law. For his special dedication in the pursuit of his professional responsibilities Mark Harmon received Special Achievement Award from the International Association Of Prosecutors in 2005.