Foreign Service Adair was posted to various economic positions in United States missions around Europe, particularly the American Embassy in Paris, France. Ambassador Adair also served as the United States Vice-Consul in Bombay, India, in 1943. In the 1960s, he was also appointed deputy secretary general of the Organization for European Economic Cooperation in Paris.
He was appointed Ambassador Extraordinary and Plenipotentiary of the United States to Panama on 6 May 1965, presenting his credentials to President Marco Aurelio Robles Méndez on 13 May 1965.
In 1966, Panamanian students demonstrating against the United States threw a milk carton filled with red paint, striking Adair in the back. But before his departure, he was able to rebuild relations between the two nations and initiate talks that ultimately led to the return of the Panama Canal to Panamanian authority.
He left the post on 6 September 1969. He was appointed Ambassador Extraordinary and Plenipotentiary to Uruguay on 15 September 1969, presented his credentials on 13 November 1969 and left the post on 28 September 1972.
He retired from the Foreign Service in 1972.
Ambassador Adair died January 22, 2006, in Falls Church, Virginia. He was 91 years old.