In 1921 he took part in the founding of the Italian Communist Party. From 1921 he was a member of the party's central committee and executive committee, siding with Bordiga during the Livorno schism. In 1927 he became a member first of the party's politburo and then of its leadership. From 1924 to 1926 he was a parliamentary deputy.
In 1944 he returned to Italy and took over the propaganda section of the Communist Party and headed the agrarian committee of the Party's central committee. He was editor of the magazine La riforma agraria. In 1946 he was elected to the Constituent Assembly and in 1948 became a senator.