Jean Cassou was born at Deusto, near Bilbao, Spain to a French father and Spanish mother, and was fluent in both French and Spanish. He studied for a license (degree) in Spanish in Paris, and received a master's degree in literature at the Bayonne Lycée. He worked for the cultural magazine Le Mercure de France; as a writer for the Ministry of State Education in France; and as an inspector of historic monuments. Along the way, he published his first novel, Éloge de la Folie (1925). In 1936, he was a member of the cabinet of Jean Zay, Minister of State Education in the Popular Front government. He broke with the Communist Party in 1939 at the time of the Nazi-Soviet pact. He joined the French Resistance in September 1940. Among the friends and colleagues who participated with him were Claude Aveline and Agnès Humbert, and they founded the Groupe du musée de l'Homme, together with Boris Vildé, Anatole Lewitsky, and Paul Rivet. With them, Cassou wrote the group's clandestine newspaper Résistance. He escaped when many members of the group were arrested by the Gestapo and took refuge in Toulouse. He worked as an agent of the "Bertaux group" but was arrested in December 1941 and imprisoned. He wrote his Thirty-three Sonnets in prison, published in 1944 under the pseudonym of Jean Noir. Cassou was released in June 1943 and continued his resistance work. In August 1944, at the time of the liberation of France by the Allies, he was seriously wounded, and spent three weeks in a coma. General de Gaulle came to his bedside to present him with the Croix de la Libération medal. In 1945, Cassou regained his post as chief of conservation at the national museums, a position he kept until 1965. In 1971, he received the Grand Prix national des Lettres and in 1983 the grand Prix de la Société des Gens de Lettres for the whole of his work.