William Benton was born in Minneapolis, Minnesota. He was educated at Shattuck Military Academy, Faribault, Minnesota, and Carleton College in Northfield, Minnesota until 1918, at which point he matriculated at Yale University, where he contributed to campus humor magazine The Yale Record and was admitted to the Zeta Psi fraternity. He graduated in 1921 and began work for advertising agencies in New York City and Chicago until 1929, after which he co-founded Benton & Bowles with Chester Bowles in New York. He moved to Norwalk, Connecticut in 1932, and served as the part-time vice president of the University of Chicago from 1937 to 1945. In 1944, he had entered into unsuccessful negotiations with Walt Disney to make six to twelve educational films annually. He was appointed Assistant Secretary of State for Public Affairs and held the position from 31 August 1945 to 30 September 1947, during which time he was active in organizing the United Nations. He was appointed to the United States Senate on 17 December 1949 by his old partner Chester Bowles (who had been elected Governor in 1948), and subsequently elected in the general election on 7 November 1950 as a Democrat to fill the vacancy caused by the resignation of Raymond E. Baldwin in December 1949 for the remainder of the term ending 3 January 1953.

In the November 1950 election, William Benton defeated Republican party candidate Prescott Sheldon Bush, father of U.S. President George Herbert Walker Bush and grandfather of U.S. President George W. Bush. In 1951 he introduced a resolution to expel Joseph McCarthy from the Senate. On television, when asked if he would take any action against Benton’s reelection bid, McCarthy replied, “I think it will be unnecessary. Little Willie Benton, Connecticut’s mental midget keeps on… it will be unnecessary for me or anyone else to do any campaigning against him. He’s doing his campaigning against himself.” Benton lost in the general election for the full term in 1952 to William A. Purtell. Benton’s comeback bid failed in 1958 when, running against Bowles and Thomas Dodd he failed to win the Democratic nomination for the U.S. Senate. He was later appointed United States Ambassador to UNESCO in Paris and served from 1963 to 1968. William Benton died in New York City on March 18, 1973, aged 72, and was survived by his widow, Helen Hemingway Benton, who died in 1974.