Giuseppe Montanari joined the studios of Roy d'Ami in 1954. There, he did an apprenticeship together with Renzo Calegari and Carl Porciani. His first jobs were illustration work, but also the comics series 'I Tre Bill', written by Roy d'Ami, for Bonelli. In 1956 and 1957, he did western stories for the magazines Cucciolo and Tiramolla.
In 1962, he went to work for La Corno, where he drew 'Atomik', as well as covers for 'Maschera Nera' and 'Gordon'. Montanari began a longtime collaboration with the publishing house RG, where he illustrated 'Goldrake il Playboy'. During the 1970s, he was present in magazines like Lanciostory ('Alamo Kid'), L'Intrepido, Corrier Boy ('Le Streghe') and Full ('Sharon Shade'), working mostly in cooperation with Ernesto Grassani.
Montanari cooperated on several magazines of the Lancio group, drawing series like 'Roaring Trio' and 'I Ragazzi di Lester'. In 1979, Montanari drew a comic about the history of the Christian Democratic Party, 'La Discussione', at DeAgostini (text by Giuseppe Pederiali). The same year, he began collaborating with Daim Press, the future Bonelli Editore. There, he illustrated several episodes of 'Il Piccolo Ranger' and 'Dylan Dog', again in cooperation with fellow artist Ernesto Grassani. From 1992, Montanari illustrates several stories with Warner Bros characters and 'James Bond Junior' with scripts by his daughter Federica for Corrierino dei Piccoli. In Il Giornalino, he drew stories with the 'Teenage Mutant Ninja Turtles', 'Il Piccolo Zorro' and 'Zia Aghata'.