Hewitt went 66-67 during his tenure at the school, including 9-22 this season and 4-14 in the Atlantic 10.
"Mason made a significant commitment to its athletic programs, especially men's basketball, when the university moved to the Atlantic 10 Conference two years ago," George Mason athletic director Brad Edwards said. "The university has high expectations for the program and thus determined a change was needed."
In his first two seasons in the Colonial Athletic Association, Hewitt led George Mason to 24 and 22 wins, respectively. George Mason did not make the NCAA tournament in any of the four seasons under Hewitt.
Hewitt was hired by George Mason in 2011 to replace Jim Larranaga, who left to take the job at the University of Miami.
- Scooby Axson