Antonelli's earliest engagements included Italian advertisements for Coca-Cola. In 1965, she made her first feature-film appearance in Le sedicenni, although her performance went uncredited. Her American debut came in 1966 in Dr. Goldfoot and the Girl Bombs. Other roles followed; her breakthrough came in 1973's Malizia. She appeared in a number of sex farces such as Till Marriage Do Us Part/Mio Dio come sono caduta in basso!.
From 1972 to 1980, Antonelli was the companion of actor Jean-Paul Belmondo. Before her relationship with Belmondo, Enrico Piacentini, a publisher, and she were divorced.
She worked in more serious films, as well, including Luchino Visconti's last film, The Innocent (1976). In Wifemistress, a romance film of 1977, she played a repressed wife experiencing a sexual awakening. Later, she appeared in Passione d'Amore (1981). Antonelli's most recent role was in the sequel Malizia 2000 (1991). She won the Italian National Syndicate of Film Journalists Award, Nastro d'Argento, in 1974 for Malizia.
On 27 April 1991, cocaine was found during a police raid on Antonelli's home. She was subsequently convicted of possession and dealing and sentenced to house arrest. She spent 10 years appealing the conviction, which was eventually overturned. In 2006, the Italian court of appeals ruled in favor of Antonelli and ordered the Ministry of Justice to pay the Actress 108,000 euros.
Antonelli died on 22 June 2015, aged 73, from a heart attack.