The church, with the original part built between 1845 and 1846 in the Gothic Revival style, was designed by Frederick Thatcher, a London-trained architect, one of the first settlers arriving in New Plymouth.

The beginnings of Christianity in the area came as a result of the need to provide the familiar spiritual and cultural institutions of home to the settlers, as well as missionary services to the Maori population.

He appointed the reverend William Bolland as Deacon for the parish of New Plymouth, allocating an existing sandstone house at Te Henui as residence for him and his family.

[4] St Mary's is one of the earliest stone churches in New Zealand, with the original part of it built between 1845 and 1846 in the Gothic Revival style.

This original part, approximately 15m by 9m, designed by Thatcher according to ideas supplied by Bishop Selwyn, has plain rubble walls, exposed timber beams, a steep-sloped Rimu roof and tall, narrow windows with pointed arches at the top.

[3] Other than a place for worship, during the First and Second Taranaki Wars, St Mary’s also became a religious redoubt, with the churchyard used as a bullock yard for transport teams.

In 1864, two years later, parallel to the existing building, it was added another aisle, designed by George Robinson, the chief builder of the original part of the church.

[4] Further enlargements were made in 1893 to the chancel, apse, sanctuary and organ chamber by Benjamin W. Mountfort, a well-known church architect.

At the same time the northern transept was enlarged as a memorial to Archdeacon Govett, under construction professionals George Edmund Tole and Horace Lovell Massey.