In 1929, Michel Saint-Denis together with some other members of the Copiaus and with the help of Copeau, moved to Paris and set up the Compagnie des Quinze, transporting Copeau's teachings on international stages to wide acclaim. In 1935, he accepted an invitation to London, where he founded the London Theatre Studio together with George Devine and Marius Goring, an actor school where he introduced Copeau's and his own concepts from his earlier experience in France. Working together with established actors like Alec Guinness, Peter Ustinov, Michael Redgrave, John Gielgud or Laurence Olivier, he soon became known as a renowned director. At one time, he also co-directed the Royal Shakespeare Company.
During World War II, he directed the French programme of the BBC ("Radio Diffusion Française") under the pseudonym of "Jacques Duchesne". After the war, Saint-Denis founded a new theater school at the damaged Old Vic that existed from 1947 to 1952.
In 1952, Saint-Denis accepted a call by the Centre Dramatique de l'Est first at Colmar, and then—since 1953—at Strasbourg, where he founded the Ecole Supérieure d'Art Dramatique. After his retirement for health reasons in 1957, he taught at the Juilliard School in New York, where he instituted the Juilliard Drama School, and served as an advisor to the Canadian National Theatre School. In 1961, he was named artistic advisor at the new Royal Shakespeare Company.
Having suffered from health problems for a long time, Michel Saint-Denis died in 1971 in London from a stroke.