Benoît Magimel was born in Paris on 11 May 1974. His mother was a nurse and his father worked in a bank. Through his maternal grandfather he is of Hungarian Jewish descent. He has a brother, Arnaud, and a sister, Bénédicte.
In 1988, he landed his first film role in Étienne Chatiliez's comedy Life Is a Long Quiet River, in which he played Maurice "Momo" Groseille. At sixteen, while in première (the second year of lycée), Magimel left school without a diploma to pursue acting as a career.