Designed by Thomas Duff on the model of King's College Chapel, Cambridge. As at Armagh Cathedral, Duff died before completion and the interior was completed by J.J. McCarthy. The later tower of 1903 was modelled on another English church, this time Gloucester Cathedral by G.C. Ashlin.

It was proposed to build the tower further down, half-way along the nave so as to conserve the grand Cambridge-like main façade, but the work involved in altering the church to accommodate it proved unfeasible.

The entry screen in Perpendicular Gothic has weathered badly due to the sandstone used. It was designed by Thomas Turner.