It was erected as part of the Vicariate Apostolic of Central Oceania in 1842, had subsequent name changes in 1937 and 1957 before being elevated to the Diocese of Tonga on June 21, 1966.

[1] Its cathedra is found in the Cathedral of the Immaculate Conception (Tongan: Malia Tupu 'Imākulata) in the capital Nuku'alofa.

It is immediately exempt to the Holy See and not part of an ecclesiastical province.

On 4 January 2015, Pope Francis announced that he would make Tonga's bishop, Soane Patita Paini Mafi, a cardinal on 14 February of that year.

[2][3] Along with the rest of the country, in the early Twenty-First Century the tiny Catholic community of some 15,000 has been considered threatened with the loss of its home due to climate change.