This Portico is composed of eight Corinthian columns of Oamaru stone (six in front, two behind), whose pedestals rest on elongated plinths, and a high pediment closely reflecting those of a Roman or Greek temple.

The interior is richly decorated, with two impressive ranges of carved limestone Corinthian columns creating colonnades along the nave, completed by the pressed zinc ceilings, wooden pews and religious sculptures.

The design is technically accomplished and forms a vital element in Petre's Basilican architectural ouvre and the building is among his most well known and iconic works.

"[5] The inspiration and effort behind the building of St Patrick's came from Father (later Monsignor) John Mackay, who became Parish Priest in Oamaru on 3 March 1890.

On an earlier trip to Europe, he had seen buildings he considered would suit the needs of the Oamaru Parish and he had commissioned Francis Petre to put his observations and ideas into a practical design.

[6] In 1898, the coffer type ceiling that was originally designed in wood panels and mouldings, was completed in zinc supplied by Wunderlich & Co. of Sydney, New South Wales.

The richly embossed zinc, while giving an impression of massiveness, was actually light and had the advantage of being an excellent resonator, greatly improving the acoustic of the Basilica.

[6] McKay, who was unremitting in his efforts to complete the building, pressed on with fundraising by means of bazaars and raffles to finance the next stage of the construction.

Monsignor McKay, the driving force behind the whole concept from start to finish, was by now celebrating the golden jubilee of his ordination and on the day, was highly praised for his untiring work over so many years on the basilica project.

[6] In 1915, a highlight in the Basilica's history had been the installation of a positive pipe organ "which added greatly to the meaning of the services as well as enhancing the skills of the choir.

"[6] There have been minor alterations and additions to the Basilica in the ensuing years, such as removal of the main altar, the stone communion rails, the stone pulpit, the addition of confessionals, under floor heating and the removal of the slate roof and its replacement with long run iron, but these cosmetic changes have detracted little for the original design of the church.