After running away from home at the age of twelve to work in a circus, he attended the local grammar school in Rimini, earning at the same time his first money as a caricaturist of famous actors and vacationers.
From the early months of 1938 he began working with the "Domenica del Corriere", which published a number of his comic sketches. In January 1939 he moved to Rome with his mother, with the excuse of studying Law at the university; instead he started working for "Marc'Aurelio", a satirical magazine, becoming popular through hundreds of sketches signed "Federico".
Before the outbreak of the war he became friends with Aldo Fabrizi writing monologues for him, and collaborated with a radio variety where he met young actress Giulietta Masina (1921-1994), whom he married in October 1943. They will only have one son, who died a month after birth.
By participating to the scripts of Fabrizi's films, he began his adventure in the cinema as an author and screenwriter of great movies, including "Roma città aperta" (1945) and "Paisà" (1946) starting a fruitful friendship with Roberto Rossellini.
He became associated with playwright Tullio Pinelli, and they became among the most popular scriptwriters of the time, working with Pietro Germi and Alberto Lattuada. The latter wanted him as an assistant director in Luci del varietà (1950).