Ulliel was born in Knightsbridge, England to a runway show producer mother and a famous clothes designer father. He has a scar on his cheek as a result of a dog's scratch from when he attempted to ride the dog like a horse when he was six years old. He says it increases his emotional acting abilities because it looks like a dimple. Ulliel attended the University of Saint-Denis, where he studied cinema. He began acting while he was still at school, appearing in 'Une Femme En Blanc', a film for French television. He also performed at the Cours Florent, where he was discovered by Les égarés director André Téchiné.

Since then, he has starred in a number of television productions, including La Bascule, Juliette, Julien L'apprenti and Le Refuge. Ulliel's first film was Alias, in 1999. Since then, he has become increasingly popular including his small role in "Brotherhood of the Wolf", and was nominated for a César Award (Best Young Male) in 2003 for Embrassez qui vous voudrez, and in 2004 for his role in Les égarés (Strayed) as the rebellious lover to a refugee during the World War. He later won the award in 2005 for his role in Un long dimanche de fiançailles (A Very Long Engagement), in which he played Manech, Audrey Tautou's character's love interest. In 2006 he appeared as a character named Gaspard in the "Le Marais" segment of Paris, je t'aime, a multi-episode film featuring an international cast and contributions from more than 18 directors. In "Le Marais", Ulliel appears alongside Elias McConnell and Marianne Faithfull.

Ulliel's most recent role is playing the young Hannibal Lecter, the title character of the prequel Hannibal Rising, which was released on February 9, 2007. Ulliel initially hesitated to audition for the role because he felt the character's popularity put pressure on whoever took the role to deliver a faultless performance. The part is his second English-language film, and the first film where he speaks English in a leading role. It has not yet been decided whether there will be another film featuring Ulliel as Lecter.

Ulliel's next role will be in a Niki Caro directed drama scheduled to film in New Zealand and France.