Joe Sinnott worked for three years in a cement factory, before he entered the Cartoonists and Illustrators School in New York City in 1949. While studying, he made his debut with the filler comic 'Trudy' in Mopsy #2 at St. Johns Publishing in 1950. He began working for Stan Lee at Timely in 1950, doing pencil and ink jobs on crime, horror, humour and superhero comics. He also drew for Dell, Charlton, Treasure Chest and Classics Illustrated. He began a fulltime collaboration with Timely/Atlas/Marvel in 1959.
There, he pencilled comics about famous persons, such as the Beatles, the Pope and Eisenhower. From 1965, he regularly cooperated with Jack Kirby on 'The Fantastic Four'. Besides this series, Sinnott has drawn for 'Thor', 'Silver Surfer', 'Captain America', 'The Avengers', 'The Hulk', 'The Defenders', and 'The Invaders'. He semi-retired in 1992, but kept doing special issues and the 'Spider-Man' Sunday page in cooperation with Alex Saviuk at King Features.