Born in Béjar, Province of Salamanca, Santonja was active in the Communist Party of Spain (PCE) in his youth, for which he was arrested in the late years of Francoist Spain. He fled to France but moved back soon after, stating that he could not stand the French people.[1] In the 1970s, he also expressed sympathy for Herri Batasuna, the political arm of ETA.[2][3] He was a close friend of communist poet Rafael Alberti and an advisor to his eponymous foundation.[3] He married Dolores Grimau, whose father Julián Grimau was executed by Franco in 1963 for running the PCE's clandestine activities in Spain.[3]