Sylvie Testud was born on January 17, 1971 in Lyon. Her parents separated when she was two years old. She spent her youth in the Lyon district of Croix-Rousse, raised by her mother, an accountant. In high school, she learned Chinese. Very early fascinated by the cinema, the young girl identifies in particular with the complexed teenager character embodied by Charlotte Gainsbourg in L'Effrontée. Having moved to Paris to study history, she soon embarked on acting by joining the free class at Cours Florent and then the Conservatory, where her teachers were Jacques Lassalle and Catherine Hiegel. She made her first screen appearance in 1994 in Couples et amants.

She decided to become an actress during her youth, after having admired actresses in films. She then took acting lessons in Lyon with the actor and director Christian Taponard. In 1989, she moved to Paris to study history, as well as drama lessons in free classes at Cours Florent, then at the National Conservatory of Dramatic Art for three years, with Jacques Lassalle and Catherine Hiegel for teachers.