Olesen, 24, took a three-shot lead into the final day at Lake Karrinyup Country Club, and eventually held onto win by as many strokes from Frenchman Dubuisson.
The Dane carded a final-round one-under-par 71, while Dubuisson (66) finished in outright second after a bogey-free round that featured six birdies.
Olesen was one over through 12 holes, but birdied the 13th and 15th to regain a commanding lead and eventually finish at 17 under.
The win marked Olesen's second title on the European circuit after his maiden breakthrough at the Sicilian Open in April 2012.
Rounding out an international top three was England's Mark Foster (69) at 12 under, ahead of a group of five tied for fourth at 11 under.
Australians Matthew Griffin (67) and Steve Dartnall (70) secured top-10 finishes, alongside Denmark's Lucas Bjerregaard (70), Scotsman David Drysdale (71) and England's James Morrison (73).
Morrison bogeyed the 18th in Perth to lose outright fourth place.
Rounding out the top 10 were Australians Wade Ormsby (66) and Richard Green (72), Italian Andrea Pavan (70), American Peter Uihlein (73), New Zealand's Ryan Fox (67) and South Korea's Kim Sihwan (75) in a tie for ninth.
South Africa's Charl Schwartzel could not launch a late challenge, shooting an even-par 72 to finish his week at nine-under overall in a tie for 15th.
It was a final round to forget for Scotland's Scott Jamieson, however, as he strung together three consecutive double-bogeys from holes two through four before throwing in another five bogeys to post an 81.