The singer was transformed into a tiger as she belted on the hit on a podium surrounded by dancers dressed in suits.
Katy Perry performs on 'The X Factor'
Flashing the flesh in a tight animal print number, Katy finished off her feline look with a pair of tiger ears.
"I get to dress up like a big cat so I love this song. I feel grrreat!" she told host Dermot O'Leary following her performance.
Katy was joined by dancers wearing suits for her rendition of 'Roar'
She also revealed she would be up for returning to the show as a judge, after previously sitting in on some auditions during the 2010 series.
The remark prompted the 1D star to propose marriage to the 'California Gurls' singer.
"I love you @katyperry ! Thank you! Ps . Will u marry me?" he tweeted.
We think Katy's current squeeze John Mayer, might have something to say about that.