Brook's modelling career began at 16 after winning a beauty competition for which her mother entered her. 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 large-breasted women. Her 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.
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 billboard of Brook's bust, said to be the largest billboard in the world.
In 2005, Brook posed for a ten-page, nude black-and-white photo spread for the photographer David Bailey, which appeared in the British design magazine Arena, in the November 2005 issue.
In 2006 she signed a contract, reported to be worth around £1m, to present Unilever's Lynx body spray, known as Axe in the US and in continental Europe. She has appeared on billboards, in newspapers, and on-line as part of an advertising campaign.
She has also appeared in commercials for Sky + & T Mobile and modelled for Reebok. In 2010, fourteen years after she started off her career as a lingerie model, she was chosen as the "new face and body" of lingerie maker Ultimo's advertising campaign.
Kelly is set to strip naked for the cover of Playboy magazine in 2010..
