He served as a member of the U. S. delegation to the 28th United Nations General Assembly, and to the Sixth Special Assembly, having ambassadorial rank with each appointment. He was a member of the U. S. delegation to the U. N. Human Rights Commission (1978–1980), was ranking Republican to the Commission on Security and Cooperation in Europe, and was a member of the U.S. Delegation to the Belgrade Conference on the Helsinki Accords. Largely due to his liberal record and support of civil rights, Buchanan became very popular in his district, even though Democrats continued to hold most local offices in the district well into the 1980s. He was reelected seven times, rarely facing serious opposition. In 1978, however, he was challenged in the primary by a considerably more conservative Republican, Albert L. Smith Jr., a longtime party activist in the Birmingham area. Buchanan fended him off but was defeated in a rematch in 1980.