Hall served as the Head of Division for the European Secretariat of the Cabinet Office from 2003 to 2006.[1] He was the Deputy Head of Mission in Bucharest from 2007 to 2008,[3] and served as the Defence Counsellor in the British Delegation to NATO from 2008 to 2012.[3] He headed the Counter Proliferation Department from 2012 to 2015.[3]