The 25-year-old closed with a four-under par 68 for a 20-under total of 268, ahead of compatriot Jazz Janewattananond, who made a closing eagle in his round of 65 to take second place.
Fellow Thai Panuphol Pittayarat, who shot a final round of 66, ended the tournament third at 15-under par.
England's Justin Rose -- bidding to reclaim the world number spot from Brooks Koepka -- finished with a disappointing three-over par 75 in joint 17th position, despite two birdies in his final two holes.
Poom, a previous winner here in 2016, said he had enjoyed playing against Sweden's Henrik Stenson, whose early challenge fell away with a final round of 71.
"I am really so proud to have won here again. I love the golf course and I am so happy that I got a chance to play with Stenson," said Poom, who now has three wins on the Asian Tour and is expected to see his current world ranking of 239 markedly improve.
Rose endured a nightmare start when he made a double bogey on the par-five second hole after needing two chips to get on to the green from the back rough. He then hit a triple bogey on the par-five 12th.
"Even if I made an eagle on the last and became the world number one, I would not have been proud of it given how I played," said a candid Rose.
"It was a very hard day. It was a shame to finish the year that way for sure, but I obviously don't want to let today change things.
But reflecting on "an awesome year", he added: "I gave it a courageous finish. I never give up and I take pride in that coming down the stretch.
"No matter if you are number one in the world or number 300, these are the moments you have to take and use as fuel. I will reflect and learn and use it as motivation."
The Asian Tour season wrapped up with India's Shubhankar Sharma winning the Order of Merit despite missing the cut, after securing the victory before the tournament.