Octavius Hadfield, the 10th child and youngest son of Joseph Hadfield, silk merchant, and his wife, Amelia Caroline White, was born at Bonchurch, Isle of Wight, England, and was baptised on 6 November 1814. His marriage to Catherine, known as Kate, third daughter of Archdeacon Henry Williams, was celebrated at Rangiātea Church, Ōtaki, New Zealand, on 19 May 1852; there were 10 children of the marriage.
Much of Hadfield's early childhood was spent on the Continent, at Brussels, Lille, Paris and Tours. Back in England, from 1829 he attended Charterhouse until severe asthma forced him to leave the school in 1831. In 1832 he went to Pembroke College, Oxford, but in 1833 continued ill health brought an end to formal university studies. After some months' recuperating in the Azores, he taught at a school kept by his sisters at Ventnor, Isle of Wight. But Hadfield responded to 'a duty' to become a missionary; his application to the Church Missionary Society was accepted in October 1837. As the bishop of London would not ordain him without a degree, Hadfield was admitted to deacon's orders in September 1838 in Sydney by William Broughton, bishop of Australia, and at Paihia, Bay of Islands, on 6 January 1839, he became the first priest to be ordained in New Zealand.
Hadfield studied the Māori language while teaching at the mission school at Waimate North but was unhappy at the 'worldly mindedness of the missionaries' and anxious to spread the Gospel. He responded to a request for a missionary for the Kapiti coast, where many had some knowledge of Christianity through instruction given by Māori teachers. In November 1839 he began his work at Waikanae and Ōtaki and set out to understand the culture of the people there. At Waikanae he worked with Te Āti Awa, from Taranaki, with occasional visits to those of the tribe who had migrated to Queen Charlotte Sound. At Ōtaki were Ngāti Toa and Ngāti Raukawa, who extended into Manawatū and Rangitīkei. He travelled hundreds of miles and by the end of 1841 was ministering to some 7,000 widely scattered Māori, and supervising 18 schools set up to provide an elementary European education combined with the teaching of agricultural and domestic skills. His role included peacekeeping and he quickly gained respect. An early visitor to Waikanae described the young missionary as 'a tall, straight, slender, active, sinewy, sunburnt, smiling Pākehā…an agreeable intellectual cheerful young Gentleman well up in the Māori Language, Habits and Manners'.
At first Hadfield found Te Āti Awa at Waikanae, who had been influenced by the teacher Hōhepa Matahau (Ripahau), more receptive to his teaching than Māori at Ōtaki, led by Te Rauparaha. Although never a convert, Te Rauparaha became Hadfield's firm friend and provided timber for the church at Waikanae in 1842; congregations of up to 500 came, often from a distance, to school and services. By 1843 most of the Ōtaki Māori had accepted Hadfield's teachings; within five years the station at Waikanae fell into disuse. Hadfield's task was complicated by the spiritual needs of the growing settler population at Port Nicholson (Wellington) and at Nelson, and their pressure for land. Matters came to a head with the confrontation at Wairau on 17 June 1843 and the missionary found his roles as mediator between Māori and settlers and adviser to Governor Robert FitzRoy interfering with his 'proper work'.
Constant ill health dogged Hadfield from the beginning of his mission until, late in 1844, a serious illness confined him for almost five years to the home of the Wellington magistrate Henry St Hill. Hadfield maintained contact with Māori friends, particularly through Rīwai Te Ahu, whom he had baptised and appointed as lay reader at Waikanae. At this time the new governor, George Grey, visited Hadfield almost daily and generally accepted his advice. Grey forwarded to the Colonial Office Hadfield's papers detailing Māori land tenure and tribal organisation and stressing the necessity for land purchases to be based on equity and mutual understanding. His practical plans for gradual and peaceful assimilation express the breadth of his vision for the colony as an integrated society with equality of rights and opportunity for all.
Hadfield continued his study of the Māori language, producing a number of liturgical translations and collaborating in writing A spelling book for the use of Māori children, published in 1852. He also studied theology, metaphysics and philology, and formed a firm friendship with Bishop George Selwyn, although Hadfield, as an evangelical, had reservations about the bishop's Puseyite leanings. Hadfield played a major role in the formulation of the constitution of the Church of the Province of New Zealand. Selwyn appointed him rural dean of the Western District of Wellington and Taranaki in 1844 and archdeacon of Kapiti in March 1849.
In October 1849 improved health enabled Hadfield to return to the mission at Ōtaki, which had prospered under the able direction of missionary colleagues, assisted by Māori converts. Families were living in weatherboard houses on their own allotments and Te Rauparaha was, until his death in November 1849, directing Māori in the erection of Rangiātea Church. Teachers were being trained at the central day and boarding school, where students also gained experience in agricultural techniques on land given by Māori and farmed for the upkeep of the school. Grain and other produce were grown and flax gathered by the Ōtaki community to meet an expanding market; Hadfield became known as a successful breeder of sheep and cattle.
Over the years Wellington newspapers published many letters expressing Hadfield's views on contentious issues and he had already earned the tag of 'political parson' for encouraging Māori to exercise their constitutional right to register as voters; he was bitterly opposed for this action in 1857 by Isaac Earl Featherston, then superintendent of Wellington province. However, it was Hadfield's ardent defence of his converts, Wiremu Kīngi Te Rangitāke and others of Te Āti Awa, now back in Taranaki, which was to make him for some time the most unpopular man in the colony. Grey's successor, Thomas Gore Browne, consulted the archdeacon and other experts regarding Māori land tenure and future government policy, and reported to the Colonial Office on the value of Hadfield's services. Yet the governor rushed headlong into open conflict when in March 1860, in response to settlers' pressure for land, he approved the purchase of Te Āti Awa land at Waitara despite opposition within the tribe. Churchmen led by Bishop Selwyn aligned themselves on the side of Māori tribal rights guaranteed under the Treaty of Waitangi. Hadfield made a direct and public appeal for justice to the Duke of Newcastle, colonial secretary, with three pamphlets: One of England's little wars, The New Zealand war: the second year of one of England's little wars and A sequel to 'One of England's little wars', published in London in 1860 and 1861. The clergy were concerned at the 'intemperate unwise language' used by Hadfield to express his deep anger, which resulted from his conviction that war could have been avoided. Many settlers regarded his actions as bordering on treason, especially when his influence was recognised in the petition of 30 March 1860 of Ōtaki Māori to Queen Victoria for the recall of the governor. Hadfield defended his stand at the bar of the House of Representatives on 14 August 1860.
The golden days of the Ōtaki mission began to wane in the 1850s, with a change in local economic circumstances, the effects of epidemics, and the growth of Māori nationalism. There was King movement activity in Ōtaki during the late 1850s, but the archdeacon was able to keep the community quiet as open warfare flared elsewhere. During the late 1860s he championed Ngāti Raukawa through Native Land Court proceedings. Hadfield had declined the bishopric of Wellington in 1857 on the grounds of ill health but was not ready to give up his work as a missionary. Once he had succeeded Bishop Abraham in 1870 he fostered the Māori pastorate, on the basis that a Māori ministry should be 'the ultimate aim of all missionary efforts.'
A good administrator, Hadfield had a reputation for being austere and dictatorial as he grappled with growing problems created by a rapidly expanding settler population and the need for more clergy and church buildings. He defended the Church constitution in the face of controversy and, believing religious teaching to be integral to the education of good citizens, campaigned steadfastly from 1855 for state support for all schools, secular and denominational; after the passing of the Education Act 1877, he turned to the development of Sunday schools. He also worked successfully towards the defeat in 1876 of the Wanganui Endowed School Bill which could have set a precedent for the expropriation of land vested in denominational trusts set up for Māori religious, charitable and educational purposes. In 1890 Hadfield was elected third Anglican primate of New Zealand, a post he held until his retirement in 1893. Kate Hadfield died on 8 January 1902 and Octavius on 11 December 1904 at Marton, New Zealand.
In 1850 Hadfield had expressed his sense of responsibility to his adopted country in the observation that 'every act in New Zealand must be productive of good or evil to generations to come'. A determined, bold and energetic man, Hadfield did not shrink from the acrimony directed against him as he fought for principles he believed must be put into practice. His friends remembered a courteous, reserved man, a scholar, dogged by ill health but 'a Rangitira [sic] every inch of him'.