Lenoir was first spotted by Ford Models when she was just 16 years of age. In 2001, Lenoir signed with L'Oréal, and has since appeared in their advertisements alongside supermodel Laetitia Casta and long-term model and actress Andie MacDowell. She has also worked for Victoria's Secret, Gap, Next, and many others. Lenoir is currently the face of UK high-street retailer Marks & Spencer, and can be seen in various British magazines and billboards alongside fellow models Twiggy and Laura Bailey.

More recently, Lenoir also appeared opposite Pierce Brosnan and Salma Hayek in the film After the Sunset, as well as in Rush Hour 3, for which she shaved her head bald. In early 2007 she was seen sporting a short bleached haircut.