Born in Fontana Liri, a small village in the Apennines, Mastroianni grew up in Turin and Rome. During World War II he was interned in a Nazi prison, but he escaped and hid in Venice.

In 1945 he started working for a film company, and began taking acting lessons. His film debut was in I Miserabili (from Victor Hugo's Les Misérables) in 1947.

He soon became a major international romantic star, starring in Big Deal on Madonna Street; and especially when Federico Fellini cast him in La Dolce Vita with Anita Ekberg in 1960.

He followed that with another signature role, that of a frustrated, womanizing film director in Fellini's 8½.

Mastroianni was married to the Italian actress Flora Carabella (1926 - 1999), who appeared in many films including "Lunatics and Lovers" and "A Night Full of Rain", from 1948 until his death; they had one child, Barbara.

He also had a daughter, Chiara Mastroianni, with his longtime mistress, the actress Catherine Deneuve; both Flora and Catherine were at his bedside when he died of pancreatic cancer at the age of 72.