New Zealand was not British, but some New South Wales governors, notably Lachlan Macquarie, exploiting a possible ambiguity in their instructions, had in fact tried to extend British authority across the Tasman, seeking to foster the commercial life of New South Wales, to protect the Maoris from vicious influences, and to support the missionaries. Macquarie, in 1814, made Kendall a Resident Magistrate; in 1819 he commissioned the missionary Butler a Justice of the Peace and declared New Zealand a dependency of New South Wales. A British statute of 1817 empowered Macquarie to punish offences committed there, though it also declared New Zealand to be not a British colony. By the 1820s Australians were starting to plan colonies in New Zealand, and in 1823 the jurisdiction of the Courts of New South Wales was extended to New Zealand (for crimes committed by British subjects). These actions did not alter the status of New Zealand, but they did show that she was a matter of concern to New South Wales officials and, to a lesser extent, to the United Kingdom.

Events in the 1830s made it certain that New Zealand would become British. In 1831 the scandalous conduct of Capt. Stewart of the Elizabeth in aiding Te Rauparaha in one of his more bloodthirsty exploits outraged respectable opinion in New Zealand, Sydney, and London. The Colonial Secretary, Lord Goderich, was appalled. In the same year, the presence of a French ship at the Bay of Islands led to fresh rumours of French colonisation and a petition from some chiefs to the King for protection against the “tribe of Marion”. But the upshot was, initially, trivial and ill-contrived. James Busby, an Australian free settler, was appointed Resident by Goderich without consulting the Governor of New South Wales. Thus relations between Governor and Resident were permanently bedevilled. Further, Busby quite lacked any authority other than support he could enlist from chiefs and missionaries. Imperial legislation to increase his powers was contemplated but never passed.

Nevertheless, the mid-1830s continued the movement towards annexation. In 1834 troops intervened for the first time to rescue the captured crew of a wrecked vessel. A year later Busby learned of Baron de Thierry's fantastic plans for the creation of a personal monarchy and secured a Declaration of Independence from 35 northern chiefs. When, in 1837, de Thierry and about 100 followers landed, the hollowness of his pretensions became apparent. In the last three years of the decade the pace quickened. Land speculators from Sydney were making large “purchases” and disputes over land between Maoris and settlers became acrimonious. An increasing number of escaped convicts crossed the Tasman. Over 200 British residents of New Zealand petitioned the Imperial government for protection of property. In 1837 Captain William Hobson was sent on a tour of inspection on HMS Rattlesnake. He recommended the establishment of “factories” (i.e., small areas under direct British rule) to protect British interests and trade. Busby, at the same time, urged that all New Zealand become a British protectorate. There were fresh scares of French initiative, thanks to the presence of French ships and the arrival of a French Catholic Bishop, Pompallier. George Gipps now Governor of New South Wales, argued that either the Residency be ended or made effective, as did the Kororareka Vigilantes Association (an experiment in self-government), and the traders and newspapers of Sydney.

In England, the government was preparing to act. A House of Lords committee favoured British possession in 1838, and in the previous year a New Zealand Association had been formed by Edward Gibbon Wakefield and his associates for the colonisation of the country. The government regarded it with suspicion, but in 1839 it (transformed into the New Zealand Company) made its intentions clear by the dispatch of an advance party aboard the Tory. By this time Hobson had already been offered the post of British Consul, and in 1839 he accepted the position of Lieutenant-Governor and Consul under the government of New South Wales. The Law Officers reported that the United Kingdom could properly annex New Zealand, and Gipps's commission was enlarged with this step in view.

The stage was set for annexation, though the official actors moved with a circumspection not equalled by private interests. The New Zealand Company had sent the Tory in haste to buy land before annexation should introduce a Crown monopoly of land purchases; Sydney “land sharks” drove bargains with Maoris in Sydney for immense areas “acquired” upon trivial considerations – the most ambitious was W. C. Wentworth, who claimed to have bought 20 million acres. Gipps's counter measures were effective; land dealings were prohibited, and past transactions were to be subjected to an official inquiry. Early in 1840 Hobson arrived in New Zealand, Lieutenant-Governor of a colony yet to be acquired. His instructions required him to take possession of the country only with the consent of the Maori chiefs. This emphasis upon consent arose from the influence of evangelical Christian views, especially as urged by the Church Missionary Society and its secretary, Dandeson Coates, upon the Colonial Office. It represented an attempt to combine the extension of British authority with a policy designed to safeguard the well-being of the native people. The Treaty of Waitangi of 6 February 1840 was the instrument of such consent, for the chiefs who signed it agreed to place themselves under the sovereignty of the Queen in return for her protection. After the initial signing Hobson annexed that part of the country down to 36°S, and apparently planned a progressive southwards annexation as signatures were collected. The resident missionaries of the Church Missionary Society were a numerous body whose cooperation was essential to the Government. Together with the Wesleyans, they assisted Hobson in urging upon the chiefs the acceptance of the treaty. Some even were dispatched southwards in the Herald to collect further signatures, normally cementing the new relationship with gifts. Hobson was forced into greater speed by the action of the newly arrived Company settlers at Port Nicholson (Wellington) in organising their own government, and possibly by a renewed threat of French intervention — the ships carrying the French settlers who were to colonise Akaroa had arrived. On 21 May Hobson issued two proclamations announcing British sovereignty over the whole country, the North Island by right of cession, the two southern islands, where the Maori population was very slight, by right of discovery. The expansion of British influence, largely from Australia, and reinforced by the Church Missionary Society and by the New Zealand Company at the eleventh hour, had brought a new British colony into existence.