In 1947, Clements succeeded Willis as governor, defeating Harry Lee Waterfield, Chandler's preferred candidate, in the Democratic primary. As governor, Clements raised taxes and used the revenue to increase funding for the state park system and construct and maintain more roads. He also achieved advancements in education, including some progress toward desegregation. In 1950, Clements was elected to the U.S. Senate. He resigned as governor to accept his Senate seat. While in the Senate, he served as Democratic party whip under party leader Lyndon Johnson and as executive director of the Senate Democratic Reelection Committee from 1957 to 1959. He was defeated by Thruston Morton in his re-election bid in 1956; a lack of support from Chandler (then serving his second term as governor) contributed to Clements' defeat. At Johnson's insistence, Clements resumed chairing the Senate Democratic Reelection Committee in 1957 and 1959.