Immediately prior to his appointment in the Department of State, Ambassador Williamson served as the Acting Special Assistant to the President and Senior Director for Relief, Stabilization, and Development at the National Security Council. From 2003 to early-2006, he served as the Director for Stability Operations on the NSC staff.  While at the NSC, he was instrumental in developing the proposal for creation of a standing U.S. Government post-conflict response capability, which was realized with the establishment of the Office of  the Coordinator for Reconstruction and Stabilization (S/CRS) in the State Department in mid-2004.

Early in his posting to the NSC, Ambassador Williamson served a rotation in Baghdad, from April to July 2003, as the first Senior Adviser to the Iraqi Ministry of Justice. From late-2001 through 2002, he served in the UN Department of Peacekeeping Operations as the Director of the Department of Justice in the United Nations Mission in Kosovo (UNMIK), overseeing the justice and prison systems for the UN-administered province.

For 7 years before that, from 1994 to 2001, he worked as a Trial Attorney at the International Criminal Tribunal for Yugoslavia (ICTY) in The Hague, Netherlands. While at the ICTY, he supervised investigations and field operations in the Balkans, compiled indictments, and prosecuted cases at trial. Among the cases handled by Ambassador Williamson were those against Slobodan Milosevic and the notorious paramilitary leader Zeljko Raznatovic, aka “Arkan,” as well as cases arising from the Yugoslav Army attacks on Vukovar and Dubrovnik, Croatia.

Prior to joining the ICTY, Ambassador Williamson served as a Trial Attorney in the U.S. Department of Justice Organized Crime Section and as an Assistant District Attorney in New Orleans.

Ambassador Williamson holds a bachelors degree from Louisiana Tech University and a law degree from Tulane University.