The second-phase expansion of Suvarnabhumi airport was launched in a ceremony at the site by Prime Minister Prayut Chan-o-cha on Wednesday, with construction to begin in February.
The cabinet on Aug 24 approved the plan with a budget of 62.5 billion baht.
Once completed in 2019, the main gateway to Thailand will be able to handle 60 million passengers a year, an increase from 45 million at present, Airports of Thailand (AoT) president Nitinai Sirismatthakarn said at the ceremony.
The work includes a new concourse and facilities located to the south, including a tunnel to link the new structure with the existing terminal.
The project includes an automated people mover system. Construction could begin in February next year.
Suvarnabhumi was opened for limited operations in 2006, replacing Don Mueang as the main airport for Thailand. Increasing congestion at the airport has led to approval of a plan to expand the facilities. A second stage was included in the original proposal.