The artists will join JLS, Pixie Lott and Stooshe at the charity gig, which will take place at London's Royal Albert Hall on June 7.
Conor Maynard and Diversity will also perform at the event, with tickets for the show on sale now.
The proceeds will go towards the Rays Of Sunshine Children's Charity, which grants wishes for seriously ill youngsters in the UK aged 3-18 years old.
The organisation granted its first wish back in 2004 and has gone on to grant over 2,000 wishes, along with hosting a number of entertaining events and hospital activities.
Meanwhile, Adam Lambert will release his second album Trespassing in the UK on July 2. Leona Lewis is expected to release her third studio set later this year.
Watch the music video for Leona Lewis's 'Collide' below: