In 1956, President Dwight D. Eisenhower appointed Parsons as United States Ambassador to Laos, head of the U.S. embassy in Vientiane, with Parsons presenting his credentials on October 12, 1956. As ambassador to the Kingdom of Laos in the midst of the Laotian Civil War, Parsons is identified with the Eisenhower administration's support of the Royal Lao Government against the Pathet Lao. His mission to Laos ended February 8, 1958. Parsons continued to support the administration's Laotian policy in 1959-61, during which time he served as Assistant Secretary of State for East Asian and Pacific Affairs. (He assumed office on July 1, 1959, and relinquished office March 30, 1961.) Testifying to the United States Congress in March 1961, Parsons said "the responsibility of the United States in Laos is indeed a very great one, and I hope there will be no misunderstanding of our firmness and steadiness." In his 1965 book "A Thousand Days", Arthur M. Schlesinger, Jr. was highly critical of Ambassador Parsons' approach to Laos (Schlesinger favored American neutralism between the royalists and the rebels), saying that Parsons "drastically misconceived the situation". Parsons never publicly responded to this or other similar criticisms.