In 1937, London went to fight in the Spanish Civil War as member of the International Brigade. He moved to France after the defeat of the Republicans and, during World War II, was arrested by the Nazis and sent to the Mauthausen concentration camp. After the war he lived in Switzerland but soon moved with family to Prague, where he became a leading figure in the Communist Party of Czechoslovakia, and was eventually nominated deputy minister of foreign affairs in 1948. In 1951 he was arrested and became a co-defendant in the Slánský trial alongside Rudolf Slánský. London was accused of being a Zionist, Trotskyite and Titoist and sentenced to life in prison, but released in 1955 and rehabilitated in 1963.
He moved to France, with his wife, where the couple wrote L'Aveu (The Confession) about his ordeal in the Prague Trials. While the main defendants were senior to London, he gained prominence worldwide by writing the book. The book was made into a film directed by Costa-Gavras, starring Yves Montand and Simone Signoret. His wife, Lise, narrated the documentary A Trial in Prague, dir. Zuzana Justman (2002, 83min).
- Interview (in French) about his life with Lise London (Lise Ricol), his wife
-  (in Spanish) interviews and articles about Lise London