Cantarini made his film debut in the 1997 Roberto Benigni directed comedy-drama Life is Beautiful, playing Benigni's four-year-old son 'Giosuè Orefice', who is sent with his Jewish-Italian father to a German concentration camp during World War II. The film won three Academy Awards. In 1998, Cantarini was awarded alongside his Life Is Beautiful castmates with a nomination for the Screen Actors Guild Award for Outstanding Performance by a Cast in a Motion Picture and the same year he won the Young Artist Award.
His second film appearance was in the 2000 Ridley Scott-directed period action/drama Gladiator. Giorgio was cast as the son of Oscar winner Russell Crowe's character 'Maximus'.
In 2001, Cantarini appeared in the Hallmark Hall of Fame American television film adaptation of author Eric Newby's autobiographical novel Love and War in the Apennines (retitled In Love and War) as 'Slavko'.
In 2005 Cantarini competed in Ballando con le Stelle, the Italian reality television version of the series Dancing With The Stars.
