Financial terms of the deal that takes affect next season were not released.
Dietz was selected in the fifth round, 138th overall, in the 2011 NHL draft.
The Medicine Hat, Alta., native leads Western Hockey League defencemen with 24 goals and has 58 points in 72 games this season. He has 100 penalty minutes and is plus-9 for the season.
The six-foot-one, 195-pound Dietz has 131 points in 220 career WHL games.