Brook's modelling career began at 16 after winning a beauty competition her mother entered her in. Following this success she worked on a range of advertising campaigns, including for Foster's Lager, Renault Megane, Walkers crisps, Piz Buin and Bravissimo, a company that specialises in bras and lingerie for big-breasted women. Her voluptuous figure eventually caught the eye of the editorial team of the Daily Star tabloid, which began featuring her as a Page Three girl.
Brook's picture soon began appearing in other lad mags such as GQ, Loaded and FHM. In April of the same year a poll over 5,000 women for Grazia magazine considered her to have the best British female body. She also topped the 'FHM 100 Sexiest Women in the World' list in 2005, which was said to have polled 15 million people. She later ranked 5th in FHM's '100 Sexiest Women in the World 2006', 17th in 2007 and 34th in 2008 respectively.
Brook has also done a large amount of commercial swimwear, sportswear and hosiery modeling. Her work for Triumph Bras caused quite a stir because of specially-commissioned 50-foot (15 m) high billboards of Brook's bust, said to be the largest billboards in the world.