Flights operate on Mondays, Wednesdays, Fridays and Sundays, with a journey time of around two hours.
Services depart Ho Chi Minh City at 1.25 pm and arrive in Chiang Mai at 3.30 pm. Return flights leave Chiang Mai at 4.30 pm and land in Ho Chi Minh City at 6.45 pm. All times are local.
Vietjet is currently the only airline operating direct flights on the route, allowing passengers to travel between the two cities without connecting flights.
The resumed service expands Vietjet's Vietnam-Thailand network, which connects major Vietnamese destinations, including Ho Chi Minh City, Hanoi, Danang and Phu Quoc, with Thai cities such as Bangkok, Phuket and Chiang Mai.
It also provides passengers with additional connections through the airline's domestic network in Thailand.
A Vietjet representative said the expanding air network would help strengthen tourism, trade and cultural exchanges between Vietnam and Thailand.
Thailand remains a popular destination for Vietnamese travellers because of its proximity, distinctive culture and diverse cuisine.
Chiang Mai, in northern Thailand, is known for its historic temples, traditional old town and mountainous landscapes.
Ho Chi Minh City, meanwhile, offers Thai visitors shopping, dining and cultural experiences, as well as connections to other destinations across Vietnam.
