Valentine served in the North Carolina House of Representatives from 1955 to 1960. Thereafter, he was an advisor and counsel to Governor Dan K. Moore and later chaired the executive committee of the North Carolina Democratic Party (1966–1968). He was a delegate to the 1968 Democratic National Convention. In 1982 he was elected to Congress from North Carolina's 2nd congressional district and served six terms in the House of Representatives. He did not stand for re-election in 1994 and retired from elected office when his term expired in January 1995. A portion of U.S. 64 near Nashville is named for him in recognition of his public service.