He received a bachelor's degree from Mississippi State University in Starkville (then Mississippi A&M) in 1923. In 1928, Stennis obtained a law degree from the University of Virginia at Charlottesville, where he was a member of Phi Beta Kappa, and Alpha Chi Rho fraternity. While in law school, he won a seat in the Mississippi House of Representatives, in which he served until 1932. Stennis was a prosecutor from 1932 to 1937 and a circuit judge from 1937 to 1947, both for Mississippi's Sixteenth Judicial District. He was the prosecuting attorney in a case where three African Americans had been beaten and tortured for a confession; in "Brown v. Mississippi", the Supreme Court ruled that it was a clear deception of court and jury by the presentation of testimony known to be perjured, and a clear denial of due process.