 He became Chief of staff of the United Nations Transition Assistance Group (UNTAG).During UNTAG, he was the Director of the Office of the Special Representative of the Secretary-General in Namibia, Martti Ahtisaari, and responsible for co-ordination of the Mission’s day-to-day political operation.Thornberry also served as the Senior Political and Legal Adviser to UNFICYP and to UNTSO, and was Director of Administration and Management at UN headquarters for four years.