Platt began his career as a research assistant at the Washington Center for Foreign Policy Research before entering the Foreign Service of the United States in 1959. Reportedly, he was inspired to join the Foreign Service by his great-grandfather, Ambassador Joseph Hodges Choate. From 1959 to 1961, he served as vice consul in Windsor, Ontario, Canada. From 1962 to 1963, he studied the Chinese language at the Foreign Service Institute and in Taichung, Taiwan. In 1964, he was assigned as political officer at the American consulate general in Hong Kong until 1968, when he became China desk officer in the Bureau of East Asian and Pacific Affairs. From 1969 to 1971, Platt was chief of the Asian Communist Areas Division of the Bureau of Intelligence and Research. In 1971–1973, he served as Deputy Director, and then Director, of the Secretariat Staff in the Department of State. As a young diplomat, Platt accompanied President Richard Nixon on the historic trip to Beijing in 1972 that signaled the resumption of relations between the U.S. and China. Platt was assigned as chief of the political section, U.S. Liaison Office, Peking, China, 1973–1974, and then as deputy chief of the political section at the Embassy in Tokyo, Japan, 1974–1977. He returned to Washington to serve as Director for Japanese Affairs in 1977 and then served as a staff member on the National Security Council at the White House from 1978 to 1980. From 1980 to 1981, he was Deputy Assistant Secretary of Defense, International Security Affairs in the U.S. Department of Defense. From 1981 to 1982, he returned to the Department of State as Deputy Assistant Secretary, International Organization Affairs.
Ambassadorships
On July 22, 1982, President Reagan appointed Platt to succeed Frank G. Wisner as the U.S. Ambassador to Zambia. He presented his credentials on August 31, 1982 and served until he left his post on December 17, 1984 to become the Special Assistant to the Secretary of State and Executive Secretary of the U.S. Department of State. Platt stayed as Executive Secretary until February 13, 1987. On August 10, 1987, he was again appointed by Reagan as the U.S. Ambassador to the Philippines, succeeding Stephen W. Bosworth. Platt presented his credentials on August 27, 1987 and served in this role through George H. W. Bush's election as president until he left his post on July 20, 1991, after receiving his subsequent appointment by President Bush, when he was replaced by Wisner. On July 2, 1991, President Bush appointed Platt to succeed Robert B. Oakley as the U.S. Ambassador to Pakistan in Islamabad, where he remained until he left his post on November 3, 1992. He was succeeded as Ambassador by John Cameron Monjo.
Later career
Following his retirement from the State Department, in 1992 Platt began serving as the fifth president of Asia Society, a non-profit organization that focuses on educating the world about Asia. He also was a member of the Council on Foreign Relations in New York and was a member of the International Advisory Board of the Financial Times.
