Upon the death of Senator Theodore Bilbo in 1947, Stennis won the special election to fill the vacancy, winning the seat from a field of five candidates (including two sitting Congressmen, John E. Rankin and William M. Colmer). He was elected to a full term in 1952, and was reelected five more times. From 1947 to 1978, he served alongside James Eastland; thus Stennis spent 31 years as Mississippi's junior senator even though he had more seniority than most of his colleagues. He and Eastland were at the time the longest serving Senate duo in American history, later broken by the South Carolina duo of Strom Thurmond and Fritz Hollings. He later developed a good relationship with Eastland's successor, Republican Thad Cochran.