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 deal excludes the US, which withdrew from a rival Asia-Pacific trade pact in 2017.
The RCEP isn't as comprehensive and doesn't cut tariffs as deeply as the TPP's successor. But many analysts think RCEP's sheer size makes it more significant.
"Its membership includes a larger group of nations, notably reflecting the membership of China, which considerably boosts the total Gross Domestic Product (GDP) of RCEP members," according to Rajiv Biswas, Asia Pacific chief economist for analyst firm IHS Markit.
While China already has a number of bilateral trade agreements, this is the first time it has signed up to a regional multilateral trade pact.
For starters, leaders hope that the pact will help to spur recovery from the coronavirus pandemic.
"Under the current global circumstances, the fact the RCEP has been signed after eight years of negotiations brings a ray of light and hope amid the clouds," said Chinese Premier Li Keqiang.
Longer-term, Mr Li described the agreement as "a victory of multilateralism and free trade".
India was also part of the negotiations, but it pulled out last year over concerns that lower tariffs could hurt local producers.
Signatories of the deal said the door remained open for India to join in the future.
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.
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