駐日アメリカ合衆国大使
In January 1977 Armacost was selected as a member of the National Security Council to handle East Asian and Chinese affairs under the Carter administration until July 1978, when he was replaced by Nicholas Platt. Years later he was appointed to be the United States Ambassador to Japan from 1989 to 1993, Under Secretary of State for Political Affairs from 1984 to 1989, and United States Ambassador to the Philippines from 1982 to 1984, during a critical period of political upheaval during the Ferdinand Marcos presidency.