McGrath plans to continue working with the band, which has a greatest-hits CD in the works, and will fit performances and tours into his TV schedule.
McGrath, who sang the 1997 hit "Fly," has been a guest host on shows from MTV and VH1.
"This is a dream job," McGrath said Thursday. "Through the band, I did some hosting and loved it. I feel in my element. I'm diving in headfirst and hopefully people will respond."
He will work with longtime host Dayna Devon.
Lisa Gregorisch-Dempsey, the series' senior executive producer, said it was a coup to get a celebrity to cover celebrities.
"I didn't want a cookie-cutter host," she said. "There's no host like Mark on TV today, and who better to bring our viewers closer to the stars than Mark? Talk about the ultimate 'insider.'"
McGrath's debut show is set for Sept. 13.