The pair join Katy Perry just as auditions are getting underway, reported Entertainment Weekly.
"I am very excited to be joining Katy, Luke, and Ryan on American Idol. As a singer, songwriter, and producer, I feel I can bring a great deal of experience to the table. Its going to be so much fun!" Richie said in a statement.
"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 honour. It's gonna be a blast!" said Bryan.