Having studied at the École des chartes, as an archiviste paléographe (graduation 1924), he was the founder-director of the journal Vendredi and a museum curator before the Second World War.

In July 1937 he attended the Second International Writers' Congress, the purpose of which was to discuss the attitude of intellectuals to the war in Spain, held in Valencia, Barcelona and Madrid and attended by many writers including André Malraux, Ernest Hemingway, Stephen Spender and Pablo Neruda.

[2] After the War he was on the editorial board of the magazine Europe at the time of its revival in 1946; he was a curator at the Musée du Petit Palais, and (from 1959 to 1971) director of the Archives de France.

He was elected to the Académie Française on 17 May 1956 by 18 votes – including Jules Romains, André Maurois and Georges Duhamel – to succeed Ernest Seillière.

During the Second World War he was in charge of large sections of the Louvre; he succeeded in hiding some of the most famous art treasures, including The Venus of Milo near Valencay, in a chateau, in the provinces.