Scacchi was born Greta Gracco in Milan, Italy, on 18 February 1960, the daughter of Luca Scacchi Gracco, an Italian art dealer and painter, and Pamela Carsaniga, an English dancer and antiques dealer. Scacchi's parents divorced when she was four, and her mother returned to her native England with Greta and her two older brothers, first to London, then to Haywards Heath, West Sussex. In 1975 after her mother's remarriage to Giovanni Carsaniga, the family settled in Perth, Australia, where she attended Hollywood Senior High School and the University of Western Australia (UWA). She made her theatrical debut at UWA's New Dolphin Theatre in Edward Bond's play Early Morning.