China's finance ministry said the new bloc's promises include eliminating some tariffs within the group, including some immediately and others over 10 years.
There were no details on which products and which countries would see immediate reduction in tariffs.
"For the first time, China and Japan reached a bilateral tariff reduction arrangement, achieving a historic breakthrough," the ministry said in a statement, without giving further details.
The deal marks the first time rival East Asian powers China, Japan and South Korea have been in a single free trade agreement.
Despite being outside RCEP and having been in the administration that propelled the TPP, US president-elect Joe Biden - Obama's vice president - is unlikely to rejoin the TPP anytime soon, analysts said, as his government will have to prioritise handling the COVID-19 outbreak at home.
"I'm not sure that there will be much focus on trade generally, including efforts to rejoin" the TPP successor grouping, "for the first year or so because there will be such a focus on COVID relief," Charles Freeman, senior vice president for Asia at the US Chamber of Commerce said this month.
RCEP "will help reduce or remove tariffs on industrial and agricultural products and set out rules for data transmission," said Luong Hoang Thai, head of the multilateral trade policy department at Vietnam's industry and trade ministry.
The pact will take effect once enough participating countries ratify the agreement domestically within the next two years, Indonesia's trade minister said last week.
For China, the new group, including many US allies, is a windfall largely resulting from Trump's retreat from the TPP, said ING's Pang.
India pulled out of RCEP talks in November last year, but ASEAN leaders said the door remained open for it to join.