The 23-year-old won at Nudgee Golf Club as an amateur last year and returned as a freshly-minted professional to add another crown, needing two playoff holes to beat Jak Carter on Sunday.
The pair both finished 11-under, then nailed their approaches to the par-three 18th and made birdie on the first play-off hole.
Carter's (71, 71, 66, 69) awkward lie in a bunker led to a bogey when they replayed the hole, and Campbell's calm up-and-down for par proved enough for the win.
Earlier, Carter could only manage a wry smile when Campbell's (66, 68, 73, 70) 10-metre putt to win in regulation smashed the middle of the cup and rested near the hole rather than blowing right by.
Smith (eight under), who will play the NSW Open before returning to his home state for Brisbane's Australian PGA Championship later this month, birdied the first two holes to move within two of the lead.
But he bogeyed the next after overshooting a par three, then had to take a drop on the par-five fourth before slamming his putter into the bag after taking a seven when his bogey putt lipped out.
There was some trademark magic with the wedge at the turn, as Smith (67, 72, 71, 70) chipped in for birdie.
But even with a Campbell bogey he was still five shots back, and the former British Open champion followed his frenetic front nine with nine pars on the way home for a two-under 70.
Smith's misfortune left Campbell and Carter in a final group shoot-out, with Campbell eventually holding his nerve after bogeys on the 16th and 17th gave Carter hope.
Blake Proverbs finished level with Smith at eight under while Elvis Smylie was a shot back in outright fifth.
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