- Franklin Delano Roosevelt (1882-1945) was the longest serving President in US History, serving three full terms and starting his fourth when he died. No other President had even won a third term (a couple had tried — Grant and T.R. — but none were elected). And, thanks to the 22nd Amendment, no President since will be able to challenge his length of service (barring the very unlikely event of the 22nd being repealed).