Marc's father, Elie Allégret, had originally been hired by Gide's mother to tutor her son in light of his weak grades in school, after which he and his charge became fast friends. In 1895 Elie was best man at Gide's wedding.
After filming a 1927 trip to the Congo with Gide, he chose to pursue a career in the motion picture industry. His relationship with Gide ended after that trip, as Allégret found out that he preferred women after having experiences with Congolese women. They nevertheless remained close friends until Gide's death in 1951. After working and training as an assistant director, in 1931 he directed his first feature ''Mam'zelle Nitouche'' and the following year received much acclaim for his film, ''Fanny''. He went on to a long career during which he wrote numerous scripts and directed more than fifty films.