SET-listed Nok Air has made Hanoi its second destination in Vietnam.
The budget airline will start flying to the Vietnamese capital on Dec 1 after the launch of its Ho Chi Minh City service on Oct 12.
The addition of Hanoi will strengthen the carrier's return to the socialist state after a seven-year hiatus.
It also unlocks traffic opportunities arising from the advent of the Asean Economic Community later this year.
Nok Air will face growing competition on the routes as other airlines seek to increase their presence in Vietnam.
In 2008, Nok Air suspended flights to Hanoi and India's Bangalore after the services plunged the airline into the red.
The airline will initially offer four flights a week from its Don Mueang airport base to Hanoi, according to insiders.
The Ho Chi Minh City service will start with four flights a week before increasing to seven shortly afterwards.
Nok Air is offering promotional fares starting from 999 baht for one-way flights to both Vietnamese cities.
The launch of its Ho Chi Minh City service had been put off for years as the airline focused on expanding its domestic network, where it saw an assured market.
Nok Air's international service now covers only Yangon and Hefei, the capital of eastern China's Anhui province, which was launched earlier this year.
The airline will introduce a second daily flight from Don Mueang to Buri Ram on Oct 25, using Bombardier Q400 turboprops, in response to stronger demand.
All of Nok Air's domestic trunk routes and international flights are served by 189-seat Boeing 737-800 jets, which now number 19 in its fleet.
NOK shares closed yesterday on the SET at 7.15 baht, unchanged, in trade worth 12 million baht.