New Zealand never had an established church, and the largest single answer to the census religion question is now none. The Anglican, Presbyterian, Catholic and Methodist churches that arrived in the nineteenth century divided the settler population along the lines of British and Irish emigration, and all four have declined steeply since the 1960s.
The distinctive religious history is Maori. Tapu, the state of restriction attaching to persons, places and objects, and its complement noa; mana, authority or effective power, held by people and by things; and whakapapa, the genealogy that connects the living to ancestors and to atua, are the organising concepts, and they did not disappear with the missions. They operate now in contexts that are formally secular, including in law and public administration, and they are the reason a New Zealand government department may seek advice on the tapu status of a site.
Christian mission arrived with Samuel Marsden in 1814 and spread rapidly, largely through Maori evangelists rather than European ones. The mission connection to the Treaty of Waitangi in 1840 is direct: the missionary Henry Williams and his son translated the text into Maori overnight, and the divergence between the English text, which cedes sovereignty, and the Maori text, which cedes kawanatanga, governorship, while guaranteeing tino rangatiratanga, is the central legal and moral question in the country to this day. A missionary translation decision sits at the root of it.
Asian migration since the 1990s has made Hinduism, Buddhism, Sikhism and Islam significant minorities, and the Christchurch mosque attacks of 2019 changed how the country discusses religious minority safety.