In September 1971, he resigned his seat in the House to accept appointment to the Senate, temporarily filling the vacancy caused by the death of Winston L. Prouty. Stafford won the January 1972 special election to serve out the rest of Prouty's term and won reelection twice including the 1976 election against outgoing Governor Thomas P. Salmon. He served for slightly over 17 years, until his retirement in 1989. He chaired the Committee on Environment and Public Works from 1981 to 1987.