At the age of 15 De Rossi was spotted by Director Alberto Lattuada in a beauty contest. Her film debut was in Lattuada's Stay As You Are (1978), alongside Marcello Mastroianni and Nastasia Kinski. She went on to play Virna Lisi's screen daughter in La Cicala (The Cricket) in 1980, again directed by Lattuada. In 1983 she played Bradamante, the famous female warrior, in Hearts and Armour directed by Giacomo Battiato. By the mid-1980s she was gaining English-speaking roles such as the beautiful Greek slave girl Eunice in the TV mini-series Quo Vadis? and Claretta Petacci, Mussolini's mistress in the docu-drama Mussolini and I alongside the actors Anthony Hopkins (Count Galeazzo Ciano) and Bob Hoskins (Mussolini). In 1990 she played Nys, a Montmartre prostitute, in Claude Chabrol's French language film Quiet Days in Clichy, a dramatisation of Henry Miller's semi-autobiographical novel based on his time in Paris. She has worked in film, theatre and television since her debut, such as starring alongside Ray Lovelock in Raiuno's TV film Marco e Giulia - Inviati Speciali (Mark and Julia, Special Envoys).