Singer Robbie Williams and actress Ayda Williams have been married for eight years.
Tomlinson, who is a former member of the pop group One Direction, is the first judge to have also been a contestant on the talent competition show, ITV noted in a news release.
He also served as a guest judge in 2016 on Cowell's U.S. program, America's Got Talent.
"This new panel is all about optimism, everyone has a real passion for finding a new star. The three new judges bring a whole new energy and I'm excited," Cowell said at a press conference Thursday.
"For nearly 30 years, I've been touring. I've been wanting to branch out and The X Factor felt like the perfect vehicle. Ayda is my rock, she's looked after me through thick and thin. I'm looking forward to getting started as a judge!" Robbie Williams said.
"The X Factor, for me, made a lot of sense. Development of artists is something I've been interested in for a long time. Having been on the show myself I know first-hand that the live shows are like nothing else you would experience. I'm looking forward to guiding auditonees through the process," Tomlinson said.
Dermot O'Leary is also returning as the show's host in the fall.
There is still time to apply for The X Factor 2018, which means YOU could be performing on stage at the SSE Arena in front of @robbiewilliams, Ayda Williams,@Louis_Tomlinson & @SimonCowell very soon! ❌🤩🎤🎶🎈— The X Factor (@TheXFactor) July 19, 2018
APPLY HERE: https://t.co/IcHlmzaJ3q pic.twitter.com/6Nbobx9LTV