In 2015, Katie appeared on series 1 of ITV's 'Ninja Warrior UK'. She became the first female competitor to reach the final stage of the competition. In her heat, Katie placed 4th out of 50 and was one of only seven competitors who managed to complete the course. It was during the heat that she became the first woman ever to "beat the wall" on the show. In the semi-final, Katie almost fell at the 'Arm Rings' but made the recovery of the season when she managed to retrieve the ring she had lost grip of. In doing so she was able to finish the obstacle and go on to become the only female competitor to complete the semi-final course, securing herself a place in the final of the show.
Katie went on to compete in series 2 and 3 of the show, managing to complete the semi-final course for a second time in series 3 but narrowly missing out on a place in the final.
In 2017, Katie was invited to be a course tester for series 4 of the show.
In 2019, Katie was selected to represent Team Europe in an American Ninja Warrior special: USA vs The World.
Series 1: Katie's run in the heat
“This is a cracking performance so far from Katie McDonnell!”
Series 2: Katie's semi-final run
“Wow! I thought I’d seen everything from her, but this is even MORE impressive!”