In 1964 Spiers became director of NATO Affairs, serving until 1966, when he was appointed as the Political Counselor at the U.S. Embassy to the United Kingdom. In 1969 he was appointed Assistant Secretary of State for Political-Military Affairs by President Nixon, serving until 1973 when he was chosen by President Nixon to be the first U.S. Ambassador to the Bahamas. In 1974 he returned to London as Charge d'affairs and Deputy Chief of Mission, holding this post until 1977 when he was appointed by President Carter as the U.S. Ambassador to Turkey. In January 1980 he was selected to be Assistant Secretary of State for Intelligence and Research by President Carter. He was selected by President Reagan to be Ambassador to Pakistan in 1981.