They will be joined in the BBC1 contest by one-time TV fitness guru Mr Motivator. boxing champion Carl Froch and Ian "H" Watkins, who enjoyed a chart career with Steps.
The Saturday night entertainment show will tackle a range of disciplines for the series which is being hosted by One Show presenter Alex Jones later this year.
Show bosses have already said that judges will include Olympic gymnast Nadia Comaneci and the London 2012 medallist Louis Smith, who is already a seasoned veteran of celebrity shows after triumphing in Strictly Come Dancing.
Also taking part in the series will be EastEnders actor John Partridge, Loose Women panellist Andrea McLean and Amelle Berrabah - who featured in the Sugababes line-up. The list of competitors is completed by actor Bobby Lockwood who appeared in Wolfblood and Lucy Mecklenburgh from The Only Way Is Essex.
Harding said of the challenge: "I'm really looking forward, but also a little bit scared, about all the training I'll be doing - but at least it beats going to the gym."
Froch, who triumphed over George Groves to retain his IBF and WBA super middleweight titles at Wembley Stadium a fortnight ago, said: "After a fight of such magnitude it will be great for me to get my body and mind stuck straight into a new discipline.
"I am excited to learn these new skills as gymnastics, backflips and somersaults are something that have always impressed me and I have wanted to be able to do."
The competitors will train with experienced gymnasts to prepare them for the sporting challenge.
Rachel Ashdown, the BBC's commissioning executive, said: "These celebrities are embarking on a gruelling training regime combining aerial and gymnastic skills.
"They'll use them all to deliver breath-taking performances that you'd expect from the department that also produces Strictly Come Dancing."
Jane Allen, the chief executive officer of British Gymnastics, said: "This is an exciting opportunity for our sport that will enable people to view gymnastics in a whole new entertainment light."