Leaders at the Pacific Islands Forum summit in Pohnpei have agreed to grant New Caledonia and French Polynesia full membership.
The French territories have been vying for years for full membership of the regional body, which is meant to be for independent countries only.
The decision was made unanimously by the Forum's 16 member states.
In a statement, the president of French Polynesia, Edouard Fritch, called the decision historic, saying it would see greater involvement of the French Pacific territories in regional affairs.
The incorporation of New Caledonia and French Polynesia was supported by France, as well as the forum's two largest members, Australia and New Zealand.
However, there have been some fears expressed in the past that including the territories would lead to an encroachment of France into regional policy, especially considering the legacy of nuclear testing.
There has also been some opposition within the territories. In New Caledonia, some indigenous Kanaks have opposed its integration before a referendum on possible independence planned for 2018.
In French Polynesia, independence activists led by Oscar Temaru have opposed its integration under colonialism.
France's other territory in the region, Wallis and Futuna, will remain an observer at the Forum.
But the inclusion of New Caledonia and French Polynesia has raised questions about the status of other territories in the Pacific, such as Guam, American Samoa and the thorny issue of West Papua.
West Papua was discussed at the leaders' summit, but they agreed to recognise the political sensitivities of it and that the issue of alleged human rights violations should remain on the agenda.