The 28-year-old golfer recovered brilliantly from being 1-down after two holes to win three consecutive holes and beat his opponent in the grand finals of the Australian Dollar 1.75 million (approximately USD 1.25 million) event.
Kiradech progressed after winning a tense, four-hole playoff over Australia's Anthony Quayle at the end of round three.
Nitties beat fellow Australians Nick Cullen, Dimitrios Papadatos and Callan OReilly as well as England's Sam Horsfield at Lake Karrinyup Country Club before meeting Kiradech in the finals.
In the match for third place, Herbert beat Horsfield 3&1.
Asian Tour players Pavit Tangkamolprasert, Poom Saksansin, Prom Meesawat and Yi-keun Chang also played in the knockout matchplay rounds of the ISPS HANDA World Super 6 Perth.
Kiradech Aphibarnrat did not get a chance to practice at the Lake Karrinyup Country Club as he flew into Perth the evening prior to the tournament. He was the last player to enter the competition, the last player to enter the matchplay knockout rounds and the last man standing.
Kiradech has won a matchplay event in his professional career previously, at the 2015 Paul Lawrie Matchplay.
He will be competing at the Brunei Championships, an event on the Asian Development Tour, from March 7 to 10.
James Nitties' most recent professional win was the South Pacific Open Championship in 2015. He beat the field by six shots.
Prom Meesawat earned Australian Dollar 25,000 by virtue of finishing in first place after 54 holes. Sean Crocker of the United States, Lucas Herbert of Australia and Thorbjorn Olesen of Denmark split another Australian Dollar 25,000 for their tied second finish.
The Knockout Hole was played from a new tee box located approximately 80 to 90 metres from the 18th green on the right-hand side of the 18th fairway.
Kiradech said, "It has been an awesome week. In the last few months, I've been getting really close at winning a tournament and I've finally done it. Every single shot counts especially in matchplay. Every single match was tough.
"James (Nitties) was playing so well, and he was just unlucky at the end. The drive at the fourth matchplay hole was one of the best tee shots in my life so far.
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