Old St Mary'sSt Barnabas' Church and St Stephen's Chapel being inadequate for the growing population of Parnell, a decision was made to erect a new Church closer to the centre of Parnell. The
Revd Frederick Thatcher designed a cruciform church to seat 300, built across Parnell Road from where the present Cathedral stands.
Bishop Selwyn consecrated St Mary's, the third seat of his Bishopric, on 14th October 1860, and in the process created the Parish of St Mary, which he named.
The Revd George Kissling was appointed Vicar, though in failing health he resigned less than a year later, on 18th September 1861.
Various additions and alterations were made during subsequent years. However, the church was drawing not only from a substantial resident population, but also from the various institutions established by Bishop Selwyn in the immediate area.
These included St Stephen's Maori Boys' School, built in 1850 on land now occupied by Parnell School; the Church of England Grammar School, built 1855 with the formidable Dr Kinder as Headmaster, and the Orphans' Home, built 1860. Through 1883 and 1884 attempts were made to start building a Cathedral, but the Diocesan Trustees refused to guarantee usage rights to the Parish, so plans lapsed. In September 1884 the Parish made a decision to build a 1000 seat church on their existing site, and building commenced in 1886 of the Cathedral Church of St Mary, which opened in 1888.