Laetitia Casta grew up on the Mediterranean island of Corsica, which is Italian culturally but French politically; her father is Corsican, while her mother is from Normandy. She emerged as a model in the early nineties and did numerous ads for many different clothing brands - as also did a lot of Victoria's Secret catalogs - and appeared in several magazines (including, inevitably, the Sports Illustrated swimsuit issue).
She made the transition to acting by first apeparing in Asterix & Obelix Take On Caesar, a live-action film of a popular French comic book, "Asterix & Obelix." But it was her portrayal of Brigitte Bardot in the Gainsbourg (Vie heroique) that got her taken seriously as an actress, earning her a Cesar award (France's equivalent of an Oscar).
Fun fact: Ms. Casta was made the model for the statue of the allegorical female figure Marianne, the symbol of France which is duplicated all over France in front of public buildings. It is an honor few French female icons have received. Catherine Deneuve was one of them (but then, you probably figured as much).