Spieth had earlier drained a nerve-wracking two-metre putt on the last just to make the sudden-death playoff.
Then, in a dramatic climax, Spieth put his approach to three metres on the first hole of the playoff - the 18th - before Hall knocked his to less than two metres.
Displaying all the cool and class that helped him land last year's Masters and US Open crowns, 23-year-old Spieth again buried his clutch putt before Hall pushed his birdie attempt right of the cup.
Spieth's victory follows his win at The Australian in 2014 and his runner-up showing last year at the same venue.
His victory is also a big win for Open officials, with the world No.5 almost certain to return to again defend the trophy next year when the tournament moves back to The Australian.
In a major consolation for the joint runners-up, Smith and Hall secured starts at next year's British Open at Royal Birkdale, as did two-time champion Aaron Baddeley, who finished in a five-way tie for fourth at 10 under, two shots out of the playoff.
Baddeley closed with a one-under 71 and edged out Rod Pampling (70), Jason Scrivener (69), Fox (71) and third-round leader Geoff Ogilvy (73) by virtue of his superior world ranking.
After starting the day with a two-stroke lead, Ogilvy looked the likely winner for much of the afternoon before unravelling with a bogey on the par-4 15th and a catastrophic double on the easy par-5 16th.
The former US Open champion struggled off the tee all day and his hopes of a second national title - to go with his 2010 triumph at The Lakes - evaporated after he drove into the trees and couldn't get out on 16.
While he eventually signed for a disappointing 73, Hall and Smith both charged home with final-round six-under 66s to reel in Ogilvy, with Spieth closing with a nice 69.
- With AAP
