Colletti started to be known outside Italy because of a long interview with him that Marxist historian Perry Anderson published in the New Left Review in 1974.

[2] Inspired by the Western Marxist philosopher Galvano Della Volpe, he then gravitated towards communism.

He wrote the foreword for the Italian edition of Alfred Schmidt's The Concept of Nature in Marx.

[5] In 1964, Coletti left the PCI because the party's break with its semi-Stalinist past was leading towards what he called, in his view, a "patently rightward direction.

From 1996 until his death he was elected on the list of Forza Italia, Silvio Berlusconi's right-wing political party, as a member of the Chamber of Deputies (lower house) in the Italian parliament.