Grob completed his fifth Canadian Tour win at 24-under-par 264. Third-round leader Alan McLean managed just a 2-under 70 in the final round to finish three back at minus-21.
Matt Bettencourt and Joseph Lanza both shot 67 to join Josh Geary (69) in third place at 19-under-par 269.
Grob posted two birdies and two bogeys over his first five holes to remain at 18-under. He started to make his move on the lead with back-to-back birdies from the eighth at Calgary Elks Lodge & Golf Club.
'I got off to a great start,' said Grob, who is the tour's all-time leading money winner. 'You knew the course was giving up birdies and you had to keep going. It was a battle.'
The 43-year-old birdied the 12th and came back with an eagle on the 14th to get to 23-under. Grob faltered to a bogey on the 15th, but rebounded with birdies on 16 and 17 to pull away.
The win jumps Grob to fourth on the Order of Merit. The top six after the Manitoba Classic, which will be played in two weeks, get an invitation to play in the PGA TOUR's Canadian Open at the end of July.
'That is obviously a huge perk for us,' said Grob. 'I'd love to get in the Open again and see all those guys out there again.'
McLean was even-par for his round through 12 holes with a birdie and a bogey. He dropped a shot on the 13th, but rebounded with three straight birdies to move to 21-under. His birdie run was stopped by a bogey on 17, but he got that stroke back with a birdie at the last.
Marc Lawless ended alone in sixth at 16-under-par 272 after a final-round 69. Brad Heaven and Ryan Thornberry were one stroke further back at minus-15.
Derek Gillespie, Alex Quiroz, Richard Scott and amateur Kris Wasylowich shared ninth at 14-under-par 274.