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 finished on 11-under, then nailed their approaches to the par-three 18th and made birdie on the first play-off hole.
When they replayed the hole and awkward lie in a bunker for Carter (71, 71, 66, 69) led to a bogey, while Campbell's calm up-and-down for par proved enough for the win.
He's the event's first back-to-back winner since Lucas Parsons in 1997-98 and the first to defend a title won as an amateur having turned professional since Aaron Baddeley's Australian Open double in 1999-00.
Campbell's steady par at the second playoff hole saw him to victory. (HANDOUT/GOLF AUSTRALIA)
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 rocketing by.
"Last year I came from the clouds; I was in the clubhouse with four or five groups to come in," Campbell said."This week, coming in, there's a lot more expectations and obviously leading every day of the tournament."It just shows how far I've come in the last 12 months and that I'm on the right track."
Smith (eight under), in the first of four Australian appearances to finish the year, 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. He slammed 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.
"One bad swing and a bad putt there, on the fourth, just kind of killed the momentum," Smith said.
"I definitely thought I had a chance today, especially with that bit of a hot start."I don't feel like I need to go out there and reinvent the wheel or anything in the next week or so."It's nice to play four rounds of competition and feel the juices flow again.
"I'll take a bit from that."
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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