He served as dean of the Fletcher School of Law and Diplomacy (1964–1978) and “one of the country's most accomplished career ambassadors.”[2] Gullion’s last post in the State Department was as the United States Ambassador to the recently independent Congo, described as “a flashpoint of the cold war.” His first diplomatic mission was in Marseilles as a deputy consul in 1937.

He was also Chargé d'Affaires ad interim to Finland when the United States severed diplomatic relations with Finland on June 30, 1944,[3] and Deputy Director of the U.S. Disarmament Administration (1960–1961).

Gullion was stationed not only in Helsinki during WWII but also Salonika, Greece “ where he witnessed the entry of German troops into both areas and coordinated the departure of American citizens and diplomatic staff.” When he finished at the National War College, he spent three years as Consul General and Counselor of the U.S. Embassy in Saigon, Vietnam, during the war in Indochina.

[1] He graduated from Princeton University in 1935 and from the National War College in 1949.

[2] Gullion died at his home of a heart attack.