The bombing killed 85 people and injured 200 more.
Bellini, a former member of Avanguardia Nazionale (National Vanguard), was found guilty of being the fifth bomber alongside the former NAR members already convicted, Giusva Fioravanti, Francesca Mambro, Luigi Ciavardini and Gilberto Cavallini.
The massacre on August 2, 1980, was the worst of Italy’s Years of Lead of political violence.
The supreme court also upheld a six-year sentence for former Carabinieri captain Piergiorgio Segatel for throwing the investigation into the terrorist attack off track.
The court also upheld a four-year term for another defendant, Domenico Catracchia, a condo manager from Rome, for giving false information to investigators.
ANSA