[2] After several stage works, in 1966 Proietti debuted both in cinema, in Pleasant Nights, and on television, in the TV series I grandi camaleonti.

[2] His first personal success came in 1971, when he replaced Domenico Modugno in the stage musical Alleluja brava gente by Garinei & Giovannini, starring alongside Renato Rascel.

[2] In 1974, after playing the role of Neri Chiaramantesi in the drama La cena delle beffe, alongside Carmelo Bene and Vittorio Gassman, in 1976, he started a fruitful collaboration with playwright Roberto Lerici, with whom he wrote and directed his stage plays, starting with the one-man show A me gli occhi, please (Give me your eyes, please, 1976, reported on the scene in 1993, 1996 and 2000, in a memorable performance at the Olympic Stadium in his hometown).

Proietti starred in and performed the opening and closing theme song for Il Circolo Pickwick which aired on Rai 1 in 1968 and at that time, he met Lucio Battisti, who was signed with the record label Dischi Ricordi.

[7] On 1 November 2020, Proietti suffered a heart attack whilst in the hospital, having been admitted fifteen days prior for heart-related problems.

[9][10] After his death, the mayor of Rome, Virginia Raggi, arranged for the Silvano Toti Globe Theatre to be renamed after Proietti.