Mumbai-based Jet Airways, which is partly owned by the Gulf carrier Etihad, currently operates its services between Bangkok and Singapore to Ho Chi Minh and Hanoi in Vietnam under a similar pact.
Similarly, Jet Airways currently codeshares with Garuda Indonesia for flights between Singapore and Jakarta.
Code-sharing allows an airline to book passengers on its partner carriers and provide seamless transport to multiple destinations where it has no presence.
"The expanded codeshare cooperation with the two airlines further strengthens our position in Asia, allowing us to win new customers in the region and providing more options and easy connections to our existing guests," Jet Airways Chief Commercial Officer Raj Sivakumar said in a release.
Besides, Indonesia and Vietnam are strategic trade and investment partners for India and also popular tourist destinations for Indian travellers, he said.
As part of the expanded agreement, Jet Airways will place its code (9W) on Vietnam Airlines' flights operating between Singapore and Phu Quoc Island and vice versa from April 15 onwards, the company said.