The two singers got to the finals of the seventh series of the UK X Factor in 2010 and it was recently announced that they will perform at the ball at The Savoy Hotel in London on October 20.
The event, which will be hosted by X Factor's Dermot O'Leary, is expected to raise around half a million pounds for ChildLine and is being sponsored by First Direct.
Ferguson said: 'I'm so happy to be performing at the ChildLine Ball, their work with children is so essential and I feel honoured to be invited to participate with such an important cause. It should be an amazing night.'
Simon Cowell added: 'ChildLine is a fantastic cause and I genuinely believe that every child needs help and support. I'm delighted The X Factor is part of this event and I hope everyone has a great evening.'