The deal was signed in June, but three of the region's largest countries - Papua New Guinea, Fiji and Vanuatu - refused to join, saying it would harm their economies and was imbalanced towards Australia and New Zealand.
The negotiator, Tessa Te Mata, said PACER Plus was about building on existing regional trade agreements and adding to the dynamism, economic integration and trade in the region.
She said the countries that refused to join needed to work out how PACER Plus would work for them and what they wanted from it.
Ms Te Mata said she was confident the agreement's ten signatories would soon be joined by others.
"The fact that eight of the Forum Island countries have already signed up, that four more are going through their domestic approval processes says that, you know, the agreement is clearly something of benefit to the region."