Giannini began his career on stage, starring in Franco Zeffirelli's productions of Romeo and Juliet and A Midsummer Night's Dream.

After appearing predominantly on television throughout the early 1960s, he had his first lead role in a film in Rita the Mosquito (1965), the first of many collaborations with filmmaker Lina Wertmüller.

He rose to international stardom through Wertmüller's The Seduction of Mimi (1972), Love and Anarchy (1973), Swept Away (1974), culminating in his Oscar-nominated turn in Seven Beauties (1975).

[2] He has been the official Italian dubber of Al Pacino since 1975,[3] and has also dubbed Jack Nicholson, Michael Douglas, and Helmut Berger.

In 1952, Giannini and his family moved to Naples where he received a diploma in electronic engineering at the Alessandro Volta Technological State Technical Institute.

During his teen years, he moved to Rome and studied at the Accademia Nazionale di Arte Drammatica Silvio D'Amico.

Giannini made his stage debut at the age of 18, opposite Lilla Brignone in In memoria di una signora amica, directed by Giuseppe Patroni Griffi.

In addition to Seven Beauties and Swept Away, he also appeared in The Seduction of Mimi, Love and Anarchy, A Night Full of Rain, and Francesca e Nunziata.

His fluency in English has brought him a number of featured roles in Hollywood productions, most notably as Inspector Pazzi in Hannibal.

[19] He also dubbed Jack Nicholson's voice as Jack Torrance in the Italian release of The Shining and the Joker in Batman and Michael Douglas as Gordon Gekko in Wall Street and the 2010 sequel as well as dubbing other actors such as Dustin Hoffman, Gérard Depardieu, Ryan O'Neal, Jeremy Irons, Mel Gibson, Tim Allen, Leonard Whiting and Ian McKellen in some of their work.