Jean Cassou was born at Deusto, near Bilbao, (Spain). His father was French (with a Mexican mother) and his mother Milagros Ibañez Pacheco was from Andalucia (Spain).His father, who had the prestigious degree Ingénieur des Arts et Manufactures, died when Jean was only sixteen. His mother gave Jean and his sister basic Spanish culture, and he learnt French and Spanish classics side by side at school. Jean did secondary studies at the Lycée Charlemagne while providing for the needs of his family, then began study for the Licence d'espagnol (Spanish) degree at the Faculty of Letters in Paris. This he followed in 1917 and 1918 by getting a Masters degree at the Bayonne Lycée and, though interrupted many times, was not mobilised in World War II. He was Secretary to Pierre Louÿs, writing from 1921 to 1929 his monthly chronicle "Spanish Letters" in the cultural magazine Le Mercure de France (of which he was editor). He became in 1923 the writer for the Ministry of State Education and in 1926 published his first novel.
In 1932 Jean Cassou became an inspector of historic monuments. In 1934 he became a member of the Vigilance Committee of anti-fascist intellectuals and director from 1936 of the review Europe. In 1936 he was a member of the cabinet of Jean Zay, Minister of State Education and of the Art-schools of the Popular front. He was then in favour of the Spanish Republic and socialism, and approached the communist party - but broke with then in 1939 at the time of the Germano-Soviet pact. On the approach of the German army, he went to the castle at Compiègne and devoted himself to the safeguard of the national heritage.
Relieved of his post as conservator at the Museum of Modern Art by the Vichy régime, he joined the Resistance in September 1940, writing its first leaflets. Among his friends who shared his views were Claude Aveline and Agnès Humbert and they founded the clandestine group the Groupe du musée de l'Homme, together with Boris Vildé, Anatole Lewitsky and Paul Rivet. With Claude Aveline, Agnès Humbert, Simone Martin-Chauffier and Marcel Abraham, he drafted the group's periodical called Résistance (six numbers between December 1940 and March 1941). When many members of the group were arrested, he escaped the Gestapo and took refuge at Toulouse. He was agent of the "Bertaux group" in August 1941, was arrested in December for his activities at the Musée de l'Homme and sentenced to a year in a Vichy prison where he composed in his head, there being no possibility of writing anything down, his Thirty-three sonnets composed in secret, which were published in 1944 under the pseudonym of Jean Noir.
Freed after a year in prison, he was sent by the ST to an internment camp at Saint-Sulpice (Tarn). After a month, following a plea from the Resistance to the director of ST, he was released in June 1943 and continued his active work for the Resistance using the pseudonyms "Alain" and Fournier". He became inspector of the southern zone. The provisional government of the French Republic in Algeria named him in June 1944 as Commissioner of the Republic for the Toulouse Region. In August, at the time of the liberation of the town, his car met an armed German patrol: two of his companions were killed and he was left for dead. He spent three weeks in a coma. General Charles de Gaulle came to his bedside to present him with the Croix de la Libération. Though his job was replaced he kept the title, but resigned after convalescing for a year.
In 1945 Jean Cassou regained his post as Chief of Conservation at the national museums, a post he kept until 1965. In 1971 he received the Grand Prix national des Lettres and in 1983 the grand Prix de la Sociéte des Gens de Lettres for the whole of his work. He died on 18 January 1986 and is buried in the cemetery at Thiais in Paris. He was a militant activist for the Peace Movement and brother-in-law of the philosopher Vladimir Jankélévitch.
