The 36-year-old will present the iHeartRadio Music Festival, which will be held at the MGM Grand in Vegas on September 23 and 24.
The festival will feature performances by huge stars such as Lady Gaga, Coldplay, Black Eyed Peas, Jennifer Lopez, Alicia Keys, Bruno Mars, Carrie Underwood, John Mayer, Sting, Kelly Clarkson, Usher, Jane's Addiction and Steven Tyler.
According to US website Gossip Cop, Ryan said: 'This is a once in a generation gathering of artists and fans from all over the country for a true, must-see music event.'
More artists set to appear at the festival will be announced in the next few weeks.