Mieli was a member of the Socialist Party, which led to his election as town councillor in Chianciano in 1901. He left in 1903. Mieli claimed in his autobiography that he left the Socialist movement due to the lack of sincerity and idealism in the movement. Police records, however, showed that Mielis homosexuality, referred to as manifest immorality' was well known in the local area, which would have severely inhibited his political career.
Secret police raided his flat in Rome in 1929, just a few months after he had moved to France. Mieli's friend Gino Chiappini, a typographer, and his friend Angelo Pisani were living there at the time. By 1930, police records marked him as a "dangerous socialist".