The daughter of French peasants, Mayniel grew up in an isolated village. Her parents' country house became the Allied headquarters during World War II.[2]
Her feature film debut was Les Cousins. The film's director and producer, Claude Chabrol, writes in his autobiography that he discovered her in an advertisement film for soap.[3]
From 1964 to 1968 she was the partner of the Italian actor Vittorio Gassman with whom she had a son, Alessandro, an actor too. She lived in Mexico.[2] Mayniel died on 21 July 2023, at the age of 87.[4]