WELLINGTON, New Zealand — The United Kingdom officially joined an Asia-Pacific trade group that includes Canada, Japan and nine other nations on Sunday at a meeting in New Zealand.

The trading bloc covers more than 500 million people and 15% of the global economy. For the UK, it is the most important trade deal concluded since it left the European Union more than three years ago.

Britain first announced in March that it had reached an agreement to join the bloc, created in 2018, after more than two years of negotiations. It is the first new member to join the bloc, called the Comprehensive and Progressive Agreement for Trans-Pacific Partnership (CPTPP).

Also includes New Zealand, Australia, Brunei, Chile, Malaysia, Mexico, Peru, Singapore, and Vietnam.

“We are honored to become the first new member of the CPTPP and to join this incredible community of now 12 economies spanning Asia, the Pacific and now Europe,” said UK Trade Secretary Kemi Badenoch.

“This is a modern and ambitious deal and our joining this exciting, growing and forward-thinking bloc is proof that the UK’s doors are open for business.”

Badenoch said more than half a million Britons already work for companies in the bloc’s member countries.

Shigeyuki Goto, Japan’s finance minister, said the UK would strengthen the bloc.

“The fact that this has been done in a way that upholds the high standards of the agreement sets an exemplary precedent for future accessions,” Goto said.

The deal comes as the UK looks to get more involved in the Indo-Pacific region. Critics say the deal pales in comparison to Britain’s trade with its 27-member European Union neighbours.

New Zealand Prime Minister Chris Hipkins said the UK’s joining the bloc was great news for the region.

“Trade is not only a priority for this government, it is essential to our economic recovery and to improving the lives and livelihoods of all New Zealanders,” said Mr. Hipkins.

Since leaving the European Union, the UK has also signed separate trade agreements with Australia and New Zealand.

The United States is not part of the bloc, after former President Donald Trump withdrew from its predecessor, the Trans-Pacific Agreement on Economic Cooperation. China has applied to join the bloc.