Officials at George Mason said the move is effective July 1. George Mason is currently a member of the Colonial Athletic Association, which it helped establish in 1979.
"This is an exciting time for George Mason University," George Mason President Angel Cabrera said in a statement Monday. "After careful consideration, we have concluded that joining the A-10 is the right move at the right time for Mason."
The A-10 is losing four schools from its current 17-school membership. Butler and Xavier are joining the new Big East Conference; Temple is joining schools from the former Big East; and Charlotte is moving to Conference USA.
Former CAA members Richmond and Virginia Commonwealth are in the Atlantic 10.