John Hufnagel, the Stampeders head coach and GM, made the announcement Monday, saying Mitchell will be under centre Saturday when the Stampeders host the Montreal Alouettes. Former starter Drew Tate will serve as the backup.
"In my mind it really doesn't matter who's the starting quarterback for Game 1," Hufnagel told reporters. "It's a long season, they're all going to play, and I believe they both will play well when they’re on the field."
Tate became Calgary's starter late in the 2011 season but has been plagued by injuries since then. Veteran Kevin Glenn posted a 20-8 record over two seasons as the Stampeders' starter and last year Mitchell went 3-0 when called upon.
Glenn was taken in the CFL expansion draft by the Ottawa Redblacks in December before being dealt to the B.C. Lions during last month's CFL draft.
Mitchell, entering his third season with Calgary, was 94-of-135 passing last year for 1,156 yards with 10 touchdowns and three interceptions.