He began in the Italian Socialist Party as an opponent of the reformist wing and became a founding member of the Communist Party of Italy in 1921, sitting on the fifteen-man Central Committee. During the latter part of his life, particularly during the Second World War, Bombacci allied with Benito Mussolini and the Italian Social Republic against the Allied invasion of Italy. He met his death after being shot by communist partisans and his body was subsequently strung up in Piazzale Loreto.