Jalil Lespert is the son of actor Jean Lespert, born in 1942 in Rosny-sous-Bois, and Farida Azi, lawyer of Algerian origin born in 1948 in Palestro (today Lakhdaria), in Algeria. He is the older brother of actor Yaniss Lespert.

Pushed by his mother, a lawyer, Jalil Lespert began studying law, but he changed his mind when in 1995, Laurent Cantet noticed him and cast him with his father in the short film Jeux de Plage. Subsequently, the young actor reunited with the director to shoot the TV film Les Sanguinaires in 1997. Two years later, Laurent Cantet offered him a new role, this time in the cinema, in the film Ressources Humaines. Thanks to the role of Franck, he was revealed to the general public and won the César for best male actor in 2001. In 2003, he won the prize for best new actor at the Cabourg Film Festival for his role in Vivre me tue by Jean- Pierre Sinapi. From then on, the actor made a series of films (Pas sur la bouche, Le Promeneur du Champ-de-Mars, Virgil, Le petit Lieutenant…).