He served as municipal councilor of Cosenza from 1946 to 1952, while he entered the Chamber of Deputies in 1948, with 26,000 votes of preference, elected on the lists of the Popular Democratic Front: he remained there for ten legislatures, until 1992.

In 1956, in the aftermath of the Soviet repression of the Hungarian revolution, the political ways of the PSI and the PCI separated and Mancini was called by Pietro Nenni to take care of the organization of the party.

Mancini dismissed the accusations made against him, but the Court of Palmi, on 25 March 1996, sentenced him for external competition in a mafia association.

A year later, the Court of Appeal of Reggio Calabria, on 24 June 1997, annulled the sentence for territorial incompetence, postponing all the documents to Catanzaro.

After the dissolution of the PSI, he founded the Mancini List, which aimed to bring the values of European socialism into Italian politics.