James Hutton Mackenzie was born, probably on 27 September 1849, in Thornhill, Dumfriesshire, Scotland. He was the son of James McKenzie and his wife, Margaret Hutton, members of the Free Church of Scotland. Mackenzie worked for his father, a postmaster, stationer and bookseller, until he began study for the ministry of the Free Church, first at the University of Edinburgh in 1871, and then at New College, Edinburgh, from 1876 to 1880. He did not take out a degree, but was licensed as a probationer in 1880.
On 24 July 1877 Mackenzie had married Janet Craig McKutcheon at Edinburgh. She died less than a year later, following the birth of a daughter. Mackenzie had intended to serve as a missionary in China, but the death of his wife led to a change of plan. He emigrated to New Zealand to serve with the Presbyterian Church of Otago and Southland, and was inducted to the charge of Wallacetown, Southland, on 7 July 1881. He retained a deep interest in foreign missions, church extension and education, and soon acquired a reputation for evangelical preaching and robust debating.
On 12 December 1889 Mackenzie was inducted to Lyttelton. He married Charlotte Elizabeth Johnston on 1 September 1890 at Christchurch; they were to have four daughters and a son. On 16 June 1892 he was inducted to Trinity Presbyterian Church, Nelson, where he remained until his retirement to Wadestown, Wellington, in 1916. He was active in civic affairs in Nelson and chaired the Town Schools Committee.
Mackenzie had strong convictions about the separation of church and state. In 1887 he had opposed an amendment to the Education Act 1877 which would have permitted religious instruction in school hours; he argued that this was to expect the state to do the work of the church. In 1897 he and Bishop C. O. Mules circularised parents about opening school 30 minutes late once a week. This was a skilful way of obtaining time for religious instruction without breaching the statutory requirements about the time given daily to education in secular subjects. Ninety per cent of the parents agreed. The Nelson system spread steadily from the 1930s, despite opposition from church leaders who wanted amendment of the act; it was effectively enshrined in legislation in the 1960s.
Not all Presbyterians took such a practical view. In 1913, when Mackenzie organised petitions against the campaign for Bible reading in state schools, James Gibb, the country's leading Presbyterian and the vice president of the Bible in State Schools League of New Zealand, accused him of disloyalty to the church's General Assemby. Mackenzie and his supporters, however, believed strongly in the separation of church and state: they should be mutually supportive but should not interfere in one another's sphere of responsibility.
Gibb's charges carried little weight, since Mackenzie was now one of the church's most widely respected leaders. He had worked for the union of the southern and northern churches in the Presbyterian Church of New Zealand in 1901, and had served as moderator of the General Assembly in 1910. In 1911 he was appointed clerk of the General Assembly, an office he held for 25 years. He had a unique knowledge of church law, interpreted it wisely and gave judicious advice on a wide variety of subjects, as well as showing great skill in drafting regulations. As clerk he dealt with a variety of administrative matters; reception of ministers from other churches, collation of replies to matters sent down by assembly and answering questions on legal and pastoral matters demanded much time, for the Presbyterian Church had a minimal salaried office staff. Mackenzie's concise reports, his witty interventions on points of order in assembly debates and his administrative skills did much to ensure the smooth running of church business.
Mackenzie's knowledge of Scottish and colonial church law enabled him to keep the Book of order up to date, so that it protected the church's heritage without becoming a barrier against change. He also cared greatly for the partnership between ministers and elders, helping to ensure that the Free Church pattern triumphed in the Presbyterian Church of New Zealand. His 1910 booklet on the subject put the central issues concisely.
Mackenzie was active in the Presbytery of Wellington and a regular worshipper at St John's Church, Willis Street. Physically and mentally active to the last, he embodied the best of the Free Church ethos of high standards of personal integrity, a strong sense of civic responsibility and the belief that daily work was a sacred trust, and helped to adapt it to the New Zealand context. He died at Wellington on 10 July 1949 shortly before his 100th birthday; Charlotte Mackenzie had died two months earlier.