Ambassador Clint Williamson (Ret), currently serves as the Lead Coordinator of the Atrocity Crimes Advisory Group (ACA) for Ukraine, a joint initiative of the United States, European Union and United Kingdom. He is the Senior Director for International Justice at Georgetown University.  He also serves, on appointment by the International Court of Justice, as the Presiding Arbiter of the Brčko Arbitration Tribunal in Bosnia and Herzegovina.

Previously, Ambassador Williamson served as Lead Prosecutor of the Brussels-based European Union Special Investigative Task Force (2011-2014), overseeing the investigation of atrocity crimes committed at the end of and in the aftermath of the 1999 war in Kosovo. As Special Expert to the Secretary-General of the United Nations (2010-2011), he coordinated diplomatic, policy and operational support from the UN and donor governments to the Khmer Rouge Tribunal in Cambodia.

He served as US Ambassador-at-Large for War Crimes Issues (2006-2009), during the Bush and Obama Administrations, leading US diplomatic and policy efforts to prevent and respond to mass atrocities and to further accountability for atrocity crimes globally. During his tenure as ambassador, he concurrently led US diplomatic efforts to secure transfers of detainees from the Guantanamo Detention Facility as those administrations endeavored to move toward closure of the facility.

Prior to his appointment as ambassador, he served for three and a half years at the White House on the National Security Council staff as Special Assistant to the President and Senior Director for Relief, Stabilization and Development and as Director for Stability Operations (2003-2006). During his White House posting, he served in Baghdad as Senior Adviser to the Ministry of Justice in Iraq (2003), reconstituting and leading the work of that ministry in the immediate aftermath of the US invasion. He served similarly as the functional minister of justice, heading the courts, prosecutorial services and prison system in UN-administered Kosovo during his tenure as Director of Justice in the UN Mission in Kosovo (2001-2002).

During his service as a Trial Attorney at the International Criminal Tribunal for Yugoslavia (1994-2001), he led the investigations of atrocity crimes committed by Serbian forces in the attacks on Vukovar and Dubrovnik, Croatia; by the paramilitary group led by Željko Ražnatović, aka “Arkan,” for crimes in Bosnia and Croatia, and by Serbian military and police forces for crimes in Kosovo.

He authored indictments against the accused in all of these cases, including the 1999 case against then-Serbian president Slobodan Milošević – the first ever indictment brought against a sitting head of state by an international tribunal. Prior to his posting to the Yugoslavia tribunal, Ambassador Williamson served as a federal prosecutor in the Organized Crime and Racketeering Section of the U.S Department of Justice and as an Assistant District Attorney in New Orleans. He is a graduate of the Tulane University School of Law and Louisiana Tech University.