World No.16 Thailand proved too strong for world No.3 Japanese in their 25-22, 25-18, 25-17 victory at a packed Chatchai Hall.
The Thais also defeated Japan in a relatively meaningless match earlier in the Nakhon Ratchasima tournament after they lost to the Olympic bronze medallists in a World Championship qualifying event in Japan earlier this month.
Any suggestions that the win was a fluke were silenced on Saturday when Thailand delivered a brilliant performance to shock Japan.
''I thought we could beat them 3-0 if we played according to our plan - and my players did just that,'' said Thailand coach Kiattipong Radchatakriengkrai.
''Our teamwork was great. Our serves and blocks were good. Japan also made some mistakes.''
The team will take a one-week break before returning to the training camp with their next assignment being the World Grand Champions in Japan in November.
Thailand captain Wilavan Apinyapong, 29, was voted the Most Valuable Player of the tournament.
She said the players were so proud of themselves to win the title although they began the tournament with a defeat against Kazakhstan.
The win also proves some of the older players of the team still have a lot to offer, she said.
''Some people said the team was too old after we lost the first match,'' a tearful Wilavan said. ''We prove them wrong. We fought very hard and became successful. We are still strong enough to win more titles.''
Thai volleyball chief Somporn Chaibangyang said: ''We did better than expectations.''
At Chatchai Hall, the final was a close encounter only in the first set, which was decided when Thailand scored five unanswered points to win 25-22.
The Japanese looked out of sorts in the next two sets as the hosts wrapped up the tie with 25-18 and 25-17 wins.
In the semi-finals, Thailand sealed a thrilling 3-2 win against China, who also lost to Thailand in the final in 2009 when the Thais claimed their first ever Asian title.
Having already sealed a place at the 2014 World Championship, Thailand earned a ticket to next year's World Grand Prix by reaching the semi-finals in Nakhon Ratchasima.
As for Japan, it was their second successive defeat in the final, having lost to China in the 2011 event.
Massive crowds formed a two-kilometre queue on a rainy Saturday morning to get tickets for the final. Some of them reportedly stayed overnight at the ticket booths.
Thousands of fans packed the grounds outside the 5,000-seat Chatchai Hall and spilled on to the main road for almost two kilometres by the time tickets went on sale at 9am.
Each person was allowed to purchase only one ticket. Tickets were priced at 100 and 200 baht but were resold for up to 2,000 baht each, according to reports.
In the third-place play-off, world No.10 South Korea finished third for a second straight time after they came from two sets down to defeat title-holders China 13-25, 17-25, 25-21, 25-22, 15-11.
It was the first time that 12-time Asian champions China failed to finish in the top three of the biennial tournament.