Tuan Hai put Vietnam in front after just 7 minutes skewing a clever shot past goalkeeper Patiwat Khammai.
Xuan Son threatened to widen the gap four minutes later with a header going closely wide.
Thailand managed to equalise the score before half-time thanks to Ben Davies’s long-range shot from about 20 metres.
Supachok ignited Thailand’s hopes of defending the title by beating Vietnamese goalie Dinh Trieu four minutes after the hour mark to set the final’s temporary score at 3-3.
However, the host team’s ambition was extinguished in the 82nd minute as Tuan Hai took Quang Hai’s favourable pass and drove a shot toward the far corner, resulting in Pansa’s own goal.
The second half had 15 minutes of injury time but it proved to be not enough for Thailand to turn the tables.
The hosts even conceded an additional goal seconds before the final whistle as Hai Long drove the ball into the empty net from long range to make it 3-2 for Vietnam.
With the return leg victory, Vietnam won the final match 5-3 on aggregate and clinched the overall 2024 ASEAN Cup trophy, successfully avenging their 2022 title loss against the War Elephants.