The 'Where Have You Been' singer confirmed the news on Twitter in a reply to a fan who expressed excitement about her then-rumoured performance.
"PHUCK YES I WILLLL!!! JUST FOR MY NAVY!!!!" Rihanna wrote, proceeding to retweet a series of posts from her fans regarding her VMAs appearance.
Rihanna joins a performance lineup that already includes Alicia Keys, Pink, Green Day, One Direction and Taylor Swift.
She is nominated for five awards including 'Best Female Video' and 'Video of the Year'.
Hosted by Kevin Hart, the 2012 MTV VMAs will air on Thursday, September 6 at 8pm ET.
Watch the music video for 'Where Have You Been' below: