Fifteen countries have formed the world’s largest trading bloc, covering nearly a third of the global economy.
The Regional Comprehensive Economic Partnership is made up of 10 Southeast Asian countries, as well as South Korea, China, Japan, Australia and New Zealand.
The pact is seen as an extension of China’s influence in the region. The deal excludes the US, which withdrew from a rival Asia-Pacific trade pact in 2017.
President Donald Trump pulled his country out of the Trans-Pacific Partnership shortly after taking office.
The deal was to involve 12 countries and was supported by Mr Trump’s predecessor Barack Obama as a way to counter China’s surging power in the region.
Negotiations over the Regional Comprehensive Economic Partnership began in 2012.
The deal was signed today on the sidelines of a meeting of the Association of Southeast Asian Nations (Asean), hosted by Vietnam.
Officials took turns signing copies of the agreement and showing them off on camera at the virtual summit.