He was born in Milan, the son of Gian Luigi Bonelli, the creator of Tex Willer and many other Italian comic strips.

He made his debut as a scriptwriter in 1957, with the translation into Italian of the Spanish series Verdugo Ranch, for which he wrote the final episode (artwork by Franco Bignotti).

In 1960 Bonelli wrote Il Giudice Bean, a mini-series of six adventures, illustrated by Sergio Tarquinio.

In 1977 Bonelli wrote the script of the book L'Uomo del Texas (illustrated by Aurelio Galleppini).

He was chairman of Sergio Bonelli Editore (formerly known as CEPIM), one of Italy's major comics publishers (titles include Tex, Dylan Dog, Mister No and many others).