The addition of Richie, which had been rumored for months before Variety confirmed the news Friday, comes just days before the revamped reality singing competition begins filming live auditions on October 3rd.
Ryan Seacrest will reprise his role of host on American Idol, which moves to ABC this spring after a 15-season run on Fox.
"I am very excited to be joining Katy, Luke and Ryan on American Idol," said Richie said in a statement. "As a singer, songwriter and producer, I feel I can bring a great deal of experience to the table. It’s going to be so much fun!"
Bryan, whose involvement was also made official Friday, added, "I’m excited at the chance to help some deserving artists reach their dreams. To be in a position in my career to help facilitate this along with the other judges is just a complete honor. It’s gonna be a blast!"
The live auditions will film in the midst of Perry's Witness: The Tour, which kicked off September 17th after a mild postponement. "SO excited, I feel like DANCING ON THE CEILING. Time to KICK THE DUST UP," Perry tweeted after the Richie and Bryan announcements.
The new American Idol, which ABC has promised will be "bigger, bolder and better-than-ever" than the version that bid farewell in April 2016, will reportedly begin broadcasting in March, Variety reports.