Cabot joined the US Foreign Service in 1926. Much of his early career was spent in Latin America. His first Foreign Service assignment was as a consul in Callao-Lima, Peru, in 1927. For the next eight years, he served in the Dominican Republic, Mexico and Brazil. From 1935 to 1939, he served first in the Netherlands and then in Sweden. From 1939 to 1941, he was in Guatemala. During much of World War II, Cabot worked in the State Department as assistant chief of the division of American Republics and then as chief of the division of Caribbean and Central American affairs. He was posted to Argentinaafter the war and, then, in 1947, he was appointed counsellor of the US Embassy in Belgrade, Yugoslavia. He was then appointed US Consul General in Shanghai between 1948 and 1949 and was in post when the Communist troops took over the city in May, 1949. Cabot served a U.S. Ambassador to Sweden from 1954 to 1957, Colombia from 1957 to 1959, Brazil from 1959 to 1961, and Poland from 1962 to 1965, during the Eisenhower and Kennedy administration. He was also commissioned to Pakistan during a recess of the Senate, but did not serve under this appointment. From 1953 to 1954, he also served as Assistant Secretary of State for Inter-American Affairs. There is a 27 page transcript from an interview of Cabot, discussing the Alliance for Progress, Bay of Pigs invasion, Cold War, foreign policy, and international relations during the Kennedy administration, archived in the John F. Kennedy Presidential Library and Museum. As ambassador to Brazil, 1959-61 his public relations campaigns on behalf of American business angered nationalist politicians and journalists. President Jânio Quadros of Brazil publicly rebuked Cabot for questioning Brazil's foreign policy and tolerance of the Cuban revolution. President John Kennedy recalled Cabot early in 1961. In December 1954, Cabot, in his role as U.S. ambassador to Sweden, attended the Nobel banquet and read the acceptance speech for the Nobel Prize in Literature awarded that year to Ernest Hemingway who was not present due to ill health. Following his retirement from the U.S. Department of State, he taught at Georgetown University's Edmund A. Walsh School of Foreign Service and TuftsFletcher School of Law and Diplomacy. In 1981, Tuft's John M. and Elizabeth L. Cabot Intercultural Center was named in honor of Cabot and his wife.
Personal life
In 1932, he married Vassar College graduate Elizabeth Lewis. Together, they were the parents of four children:
The Racial Conflict in Transylvania: A Discussion of the Conflicting Claims of Rumania and Hungary to Transylvania, the Banat, and the Eastern Section of the Hungarian Plain, 1926
Toward Our Common American Destiny: Speeches and Interviews on Latin American Problems, 1954
First line of defense: forty years' experiences of a career diplomat.