The Monarchs' arrival will give the C-USA 14 members in 2013, and the league is also expected to split into two divisions.
The conference sought new members after Houston, SMU, UCF and Memphis announced they were leaving for the Big East in 2013. Staying with at least 12 football members allows C-USA to continue to hold its football championship game.
ODU becomes the second school to leave the Colonial Athletic Association this week. VCU announced Tuesday that it is heading to the Atlantic 10 in July 2012.
"We saw this as a game changer for us relative to football reclassification and also a way to enhance the majority of all of our 16 intercollegiate athletic programs," ODU athletic director Wood Selig told ESPN.com. "Sometimes conference moves are all about assisting one sport, perhaps two, this was a move that greatly enhanced our national visibility and opportunities across the majority of our programs relative to competing at the highest level possible."
The Monarchs will have to pay a $250,000 exit fee and forfeiture of $400,000 in revenue distribution this year, CAA commissioner Tom Yeager told ESPN.com Thursday.