The 21-year-old, who won the sixth series of X Factor in 2009, will play the eponymous deaf, dumb and blind pinball enthusiast in a one-off charity performance of the show, which is based on The Who's 1969 double album.
Speaking to Digital Spy, McElderry admitted that while he was initially concerned about the stigma attached to X Factor winners, the choice to take a role "different to what people would expect" was more about proving something to himself.
"I didn't want to do a show that people would go, 'Oh, I knew he would do that', and when it was first announced I was doing this, everybody was a bit like, 'Wow'," he said.
"At first it was about [X Factor], but I feel like that's kind of in the past now and it's more about proving myself as a performer, proving that I'm progressing, proving that I'm willing to take risks.
"[Being in Tommy is] more for myself than anything, but also to kind of prove that... I'm trying new things and being a bit more bold with choices."
Joe McElderry with The Who frontman Roger Daltry, who played Tommy in the 1975 film version:
McElderry also spoke about his special appearance in the West End production of Thriller for Children in Need on November 15.
Confirming that he would be singing Michael Jackson's 1980 track 'She's Out Of my Life', McElderry continued: "It's a song I sung on X Factor, so it's gonna be pretty easy to just go in.
"And I kind of get to be myself in that, because it's for charity. But I might turn on a bit of the Jacko."
McElderry will appear in Tommy at the Prince Edward Theatre on Monday, November 12.
Tickets range from £15 to £50, with £65 premium seats and a £125 VIP package also available. They can be purchased from the Delfont Mackintosh Theatres website.