The 29-year-old Open champion held a three-shot overnight lead and fired a final-round three-under-par 68 to close on 14 under and secure the title for a third time.
World number three Smith, tournament winner in 2017 and 2018, made four birdies and one bogey to see off the challenge of Japan's Ryo Hisatsune and fellow Australian Jason Scrivener, who both finished on 11 under.
Hisatsune shot a final-round 65 to rise from 11th overnight and finish joint second alongside Australia's John Scrivener, who finished the final round on four under.
Hisatune's last-day charge was not enough to overhaul Smith, who made birdies at the second, 12th, 13th and 16th holes and dropped his only shot at the 11th.
England's John Parry matched Hisatune's six-under-par final round to climb from joint 20th place overnight to finish tied in fourth with Australia's Min Woo Lee.