New Plymouth was chosen as the site for New Zealand's second European colony, with settlers arriving from 1841. Most were members of the Church of England, and the Church Mission Society moved quickly to establish an Anglican presence in the new diocese -- which, at first, encompassed the entire country and islands stretching into Polynesia. In 1841, George Augustus Selwyn was appointed Bishop of New Zealand. He arrived the following year and began visiting settlements, reaching New Plymouth in October 1842. There he appointed Reverend William Bolland as deacon for the parish and began organizing church construction. He also recruited Frederick Thatcher, a London-trained architect and associate of the Royal Institute of British Architects, who had arrived in New Plymouth in 1843. Thatcher would become a key figure in developing New Zealand's Gothic Revival vernacular architecture.

Most early New Zealand churches were built from timber -- the material was abundant, the colony was young, and permanence felt like a luxury. Thatcher and Selwyn chose stone. The original structure, roughly 15 meters by 9, has plain rubble walls, exposed timber beams, a steep-pitched rimu roof, and those distinctively pointed windows that pull the eye upward in the English manner. The design was Thatcher's, working from ideas supplied by the bishop, and it was completed between 1845 and 1846. For a settlement that had existed for barely four years, it was a statement of intention: we are staying, and we are building something that will outlast us. The graveyard that grew around the church would eventually hold the remains of Bolland himself, Reverend Henry Govett (the second vicar), Captain Henry King (the resident magistrate), and other figures from New Plymouth's founding generation.

St Mary's served as a parish church for 168 years. On 6 March 2010, it was consecrated as a cathedral in the Diocese of Waikato and Taranaki, becoming the seat of the bishop. The elevation made it simultaneously one of New Zealand's oldest church buildings and one of the Anglican Communion's newest cathedrals -- a distinction that captures the peculiar tempo of New Zealand's ecclesiastical history. The building had been registered as a Category 1 heritage structure by the New Zealand Historic Places Trust on 28 June 1984, with registration number 148. Its significance was architectural as much as spiritual: in a country where wooden buildings were the norm, St Mary's represented an early and enduring commitment to stone construction that influenced church building across the region.

When the 2011 Christchurch earthquake devastated Canterbury's cathedral heritage, the tremor sent aftershocks through New Zealand's approach to historic buildings far beyond the immediate damage zone. A detailed seismic assessment of St Mary's was undertaken in 2014, and the results were sobering enough that the cathedral closed for repairs in February 2016. The closure prompted the resignation of Dean Jamie Allen, who had served since the cathedral's consecration. The building's subsequent history has been marked by an unusual rate of leadership change -- six deans in a dozen years -- and an ongoing negotiation between preservation and safety. The stone walls that Frederick Thatcher raised in 1845 were built to declare permanence, but permanence on a seismically active island chain requires constant vigilance and periodic reinvention.