The second start for the Buchanan graduate in his four years with the Bulldogs will come against USC on Friday.
The battle for the starting spot was between Mandal and Khristian Martin, who transferred from Maryland.
"He's done a tremendous job," said head coach Matt Entz on Monday when making the announcement. "He had a really good Fall camp."
Entz also noted that timing, accuracy and taking care of the ball helped Mandal win the job.
The Bulldogs are preparing for their first season in the revamped Pac-12 Conference.
Kickoff is set for 6 pm at the Coliseum on Friday.