Brook had been dating rugby player Thom Evans since December 2010. On 16 March 2011, she announced via her Twitter account that she and Evans were expecting a baby girl. On 9 May 2011, Brook suffered a miscarriage. Brook is an animal lover and posed nude with her body painted in scales for the "Whose Skin Are You In?" campaign by PETA. At end of 2013 Kelly opened her bar Steam and Rye in London. In June 2014 Steam and Rye won Bar of the Year at the London Club and Bar Awards. Brook met American actor Billy Zane while filming thriller Survival Island in Eleuthera, Bahamas in 2004. Her performances have had mixed reviews, the Daily Mail said "Kelly Brook has a pencil waist and rabbit-thigh legs, but she is not a great interpreter of a role". Brook made her full screen debut with a minor role in the film Sorted. Shortly thereafter, she appeared in the film Ripper. She played the girlfriend of Clark Kent/Superman's nemesis Lex Luthor in four episodes of the American science fiction drama Smallville during the show's first season (2001–02). She has also completed assignments as a film actress in Canada and made a short appearance as Lyle's girlfriend in the 2003 film The Italian Job.
Brook was billed as a guest judge in the episode in which she appeared, taped in Manchester and aired on 16 May. In January 2009, she joined the third series of Britain's Got Talent as a fourth judge, but was subsequently axed from the programme after less than a week on the panel, the producers having decided the four-judge format was "too complicated". In 2013, Brook became a temporary team captain on Celebrity Juice aired on ITV2. She appeared in Season 9, replacing Fearne Cotton while she was on maternity leave. In 2016, Brook served as a team captain on the Channel 5 panel show It's Not Me, It's You. She also competed in the Strictly Come Dancing Christmas Special 2008, dancing the Jive with Brian Fortuna, Brendan Cole having to compete with his later partner Lisa Snowdon. Brook and Fortuna were put into fourth place, but with the studio audience's vote they came second to Jill Halfpenny and Darren Bennett.