Born Louis Gendre, he was educated in France, Britain, and Turkey. He trained as an actor with René Simon at the École Dramatique. He debuted on-screen in 1939, going on to play cultivated, polished, dashing lead roles in a number of French romantic comedies and dramas. During World War II, after his father was arrested by the Gestapo, Louis and his two brothers joined the French underground; his film career came to a halt when he refused to act in Nazi propaganda films. In 1948, David O. Selznick invited him to Hollywood to appear in The Paradine Case; he remained in the USA and went on to star in a number of Hollywood films. After 1953, he appeared in international productions and, in 1958, appeared in Gigi, his best-known film by American audiences. His career was hampered by the limitations of the roles he was offered, most of which featured him as an old-fashioned Continental lover.
His son, Louis Henry, committed suicide by drug overdose in 1981. He was a friend of Albert R. Broccoli Part of his French Resistance work was to help publish and distribute newspapers for the Underground. Considered the best player in Darryl F. Zanuck's famous croquet circle. He moved back to France after his career in Hollywood.