Fifteen countries have formed the world's largest trading bloc, covering nearly a third of the global economy.
The Regional Comprehensive Economic Partnership (RCEP) 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 (TPP) 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.
Members of the RCEP make up nearly a third of the world's population and account for 29% of global gross domestic product.
The new free trade bloc will be bigger than both the US-Mexico-Canada Agreement and the European Union.
RCEP: Asia-Pacific countries form world'''s largest trading bloc - BBC News
Also ... Asia forms world'''s biggest trade bloc, excluding U.S.