He was a member of the French resistance/partisans during WWII. Shortly after the liberation of Paris from German occupation in 1944, he wrote Anti-Semite and Jew (original in French: Réflexions sur la question juive, literally: "Reflections on the Jewish Question"). In the book, he tried to explain the causes of "hate" by analyzing anti-Semitism.
Sartre was awarded the 1964 Nobel Prize in Literature, but he had previously stated that literature functioned ultimately as a bourgeois substitute for real commitment in the world and publicly declined it. Sartre or someone close to him is stated to have contacted the Swedish Academy in 1975 with a request for the prize money, but was refused.