Sam Buttery was a finalist in the first series of The Voice, being mentored by Tom Jones, and has since appeared in Taboo, for which he was nominated for a WhatsOnStage Award.
Darius Campbell rose to fame after competing in both Popstars and Pop Idol in consecutive years, and has since forged a West End career with roles in Chicago, Guys and Dolls and Gone With the Wind. He is soon to appear in Tim Rice's new musical From Here To Eternity.
Marcus Collins was the runner-up in the 2011 series and starred as Seaweed Stubbs in the UK tour of Hairspray earlier this year, describing it as a "dream role".
Cassie Compton, who appeared on the very first series of X Factor back in 2004, has since forged a successful musical theatre career, with West End credits including Wicked, Les Miserables and Dirty Dancing.
Brenda Edwards rose to fame on the second series of The X Factor, reaching the semi-finals. Offers of stage work soon followed and she has starred in West End productions Chicago, Carmen Jones and We Will Rock You.
Niki Evans reached the semi-finals in 2007, and has since performed on UK tours of Blood Brothers and Legally Blonde, as well as appearing in Blood Brothers in the West End.
Gareth Gates was runner-up in the first series of Pop Idol and had a successful pop career, before moving to musical theatre where shows include Joseph and the Amazing Technicolour Dreamcoat, Les Miserables, Loserville and Legally Blonde.
Ray Quinn just missed out to Leona Lewis in the 2006 series, but soon found consolation starring in West End productions of Grease and Dreamboats and Petticoats.
Rhydian Roberts, one of The X Factor's most distinctive contestants, was runner-up on the 2007 series and has since notched up a range of theatre roles including tours of We Will Rock You, Grease and The Rocky Horror Show.
Diana Vickers, who reached the semi-final of the 2008-09 series (where she was noted for her bare-footed performances), won critical acclaim playing the title role in a West End revival of Jim Cartwright's The Rise and Fall of Little Voice in 2009.
Kimberley Walsh is one fifth of Girls Aloud, one of the most successful UK girl groups, which began on Popstars: The Rivals. She has appeared in the West End in Shrek the Musical.
Shayne Ward won the second series of the show, subsequently releasing a number one single and album, and was nominated for a WhatsOnStage award for his performance in Rock of Ages.
Will Young was winner of the inaugural Pop Idol in 2002, and has since acted on screen and stage, winning a WhatsOnStage Award in 2013 for his performance as Emcee in Cabaret, a role which he is currently reprising on tour.