Gibelli was born on 27 December 1893 to an Italian family in Milan. Initially he worked at a FIAT aircraft engine factory and took part in political rallies, protesting against Italian invasion of Libya and celebrating the October Revolution. After being arrested in 1917 for participating in a "seditious" demonstrations, but he was soon released and continued to engage in politics, supporting the labour movement against the blackshirts in the Biennio Rosso. Before emigrating to Soviet Russia in 1921 due to the rise of Mussolini he was an active supporter of the Italian Communist Party immediately upon its foundation.