He began the final round only one shot back and said he was pretty comfortable as he chased his first title on Australian soil.
Geary's victory - his second from three starts since returning home from the US - sees him join an impressive list of past WA Open champions, which includes the likes of Gary Player, Greg Norman, Ian Baker-Finch, Brett Rumford and Stephen Leaney.
"It has been six or seven years now that I have been trying for a win," said Geary.
"The highest hurdle is the first one. Now I have broken through I should be good for the near future."
Geary's had a rough year and with little to no status in the US he was limited to playing mini-tour events, which offer small purses.
With his win in Western Australia Geary also earned a start in this week's Perth International.
"This means a lot right now, especially with my status," Geary said.
"It means I get a start next week which I wouldn't have had. It also assures me starts all summer. It is huge from my career point of view."
Geary came into the WA Open Championship in good form having won in his home province as well as finishing T20 at the WA PGA Championship last week.
The PGA Tour of Australasia now heads up the road to Lake Karrinyup Country Club for Australia's richest golf tournament, the Perth International.
Meanwhile, on the OneAsia Tour, Lower Hutt professional Mark Brown finished in a share of fourth at the China Masters yesterday, in a tournament that was played on the Montgomerie course of the Nanshan International Golf Club in the eastern province of Shandong.
Brown was one of five golfers at six-under for the week, three strokes back from winner Charl Schwartzel who closed the tournament with a four-under par 68 in the final round.
Kiwi Gareth Paddison finished in a share of 15th at one-under for the event, while Te Awamutu's Brad Shilton was three strokes back in a tie for 23rd at two-over.
In the United States, Danny Lee has finished in a share of 33rd at the Frys.com Open in California on the PGA Tour.
Lee carded a one-under par 70 in his final round to finish at seven-under for the tournament, 10 strokes back from eventual winner, American Jimmy Walker, who fired a five-under 66 in his fourth round. Walker finished two shots ahead of Fijian veteran Vijay Singh.
Manawatu's Tim Wilkinson, who was given a start in the tournament as an alternate, missed the cut with rounds of 71 and 72.
At the Toshin Golf Tournament on the Japanese tour, David Smail finished in a share of 19th at 13-under for the tournament, 11 strokes behind winner Yoshinori Fujimoto. North Harbour professional Michael Hendry finished at 10-under for the week in a share of 37th.
Hendry is currently 55th on the Japan Tour's order of merit in his debut season, while Smail is 62nd. The top 70 players retain their card for next year.
