The former Nancy hopeful will appear from mid-September as Meat in the show, which centres around the music of Queen.
"It is a dream part. We Will Rock You is one of my favourite shows," Tucker explained. "I first saw it when I was a student at the Royal Academy and loved it. I am beside myself with excitement. I just can't believe it."
We Will Rock You, penned by comedian Ben Elton, has become an international success since its debut in the West End in 2002.
Tucker narrowly missed out on a place in the final when she appeared on I'd Do Anything earlier this year. She had been a firm favourite of Cameron Mackintosh, who is producing the West End revival of Oliver!. The show was eventually won by Jodie Prenger.