Barco returned to Colombia in 1954 to help negotiate the peace process which allowed the formation of the National Front between liberals and conservatives, which lasted two decades. He became a member of the Senate, the upper house of Congress in 1958, left to become the ambassador to Britain in 1961, and returned to Colombia in 1962. He served another term in the Senate until 1966, when he was elected mayor of Colombia's capital, Bogotá. He served in that position until 1969, when he became a director of the World Bank until 1974. He then served as ambassador to the United States from 1977 until 1980.