Thomas Cahill was born on March 23, 1940 in Bronx, New York City, New York, USA. He was married to Susan Neunzig. He died on October 18, 2022 in Manhattan, New York City, New York, USA.
He majored in classical literature and medieval philosophy at Fordham University, receiving a bachelor's degree. He studied for the priesthood before deciding against it. At Columbia University he studied film, receiving a master's degree.