From an early age, Marais set his heart on becoming an actor, although he received no encouragement from his family. Having failed a screen test for Jean Tarride's film Étienne, and having being turned down by the Paris Conservatory, he took acting classes with Charles Dullin. He scraped a living by doing odd jobs and taking on bit parts in the theatre.
Marais' first stroke of luck came in 1937 when he met Jean Cocteau, the legendary French writer who would become a life-long friend of Marais and to whom Marais would owe most of his success. Cocteau gave Marais his first substantial acting job, a non-speaking part in his stage play Œdipe-Roi . The following year, Cocteau cast Marais as the Knight Galahad in Les Chevaliers de la Table Ronde.
During World War II, Marais made his big break in cinema, appearing in Jean Delannoy's 1943 film L'Éternal retour (after a personal recommendation from his friend Cocteau). This was the turning point in Marais' life, and the start of a film career which was to span nearly sixty years.
Having appeared in Cocteau's legendary films La belle et la bête and Orphée, Marais would become one of the most admired and celebrated actors of his generation. In the next two decades, the kind of role he would become mostly associated with was that of the dashing sword master, dazzling his audience in some impressive French swashbuckling adventures. This include, amongst others: Le Comte de Monte Cristo (1955), Le Bossu (1959) and Le Capitaine Fracasse (1961). He also appeared opposite the awesome comic genius Louis de Funès in the Fantomas series of films in the 1960s. Marais was equally impressive in theatre, appearing in such plays as Britannicus, Pygmalion and Cher Menteur.
Marais continued an active career on stage, film and television well into his eighties. When he was not acting, he indulged in other creative pursuits, which included painting, poetry and sculpture. Marais' sudden death in Cannes in November 1998, at the age of 85, shocked the French nation, but it served as a reminder of the immense contribution that he made to drama in general, and to French cinema in particular.