They will join X Factor runner-up Olly Murs and Nicole Scherzinger, who were also announced as this year's headliners.
All the acts will perform on the first night of the inaugural music event on Saturday, December 4, held at London's O2 Arena.
They will perform alongside recently-confirmed acts Black Eyed Peas, Cee Lo Green and The Script.
Performers for the Sunday, December 5 show are expected to be announced later this week.
Last year's festive concert, hosted by radio station Capital FM, included sets from Lady GaGa, Backstreet Boys, Sugababes and Miley Cyrus.