The Australian came from behind to defeat Japanese rival Go Soeda, who was seeded No 6, 5-7, 7-5, 6-1 to take the men’s singles title.
Thompson who finished second last year, has secured 7,200 USD in prize money and 90 points to add to his world ranking.
Earlier in the doubles event, Sa Ratiwatana and So Ratiwatana of Thailand beat Jeevan Nedunchezhiyan and Ramakumar Ramanathan of India 7-5, 6-4 to take the trophy.
The Vietnam Open is a professional tournament played on hard courts. It is part of the 2016 ATP Challenger Tour with a bonus of 50,000 USD for the winners.
