"I'm delighted to be returning to The X Factor as I just love the gig," O'Leary said. "I hope The X Factor 2012 continues to bring a sense of fun to Saturday and Sunday nights and gives the nation a show that they can laugh, cry and sometimes scream at."
X Factor boss Simon Cowell added: "Dermot has done a brilliant job for the past five years - he is Mr X Factor."
ITV Director of Television Peter Fincham also said: "Dermot is a class act; we're delighted to have him as the host of The X Factor. He's a valuable part of what makes the show popular with viewers."