The current building, designed by architect Joseph Welland in the Norman Romanesque style, complete with a three-stage tower, pyramidal spire, rose window, and rounded apsidal east end, replaced a medieval structure that had itself been enlarged and altered repeatedly over the centuries. What makes the site quietly remarkable is not the Victorian building but the accumulated layers of use, inscription, and erasure that lie beneath and around it, each generation leaving its own mark before the next swept most of it away.

The church is first recorded in an inquisition of 1201 to 1202, and Bishop Donatus O'Brien's ordinance of 1204 to 1206 specifically describes it as being within the city of Limerick, indicating it already sat inside the town walls. A bequest of 6s. 8d. was left to it by Geoffrey Galwey in 1445, placing it among the recognised parish churches of the medieval city. Thomas Dineley, who toured Ireland in 1680 and sketched what he saw, recorded a church with two aisles, Gothic tracery in the east windows, a double bell-chamber on the east gable, and, in the north wall, a single lancet and a pointed door. Before the building was substantially altered in 1763, using five hundred pounds raised by parishioners and pew sales, it contained a monument to Thomas Power and his wife Joanna Rice, dated 1622, surrounded by carved figures of the twelve Apostles. The monument carried a verse common to funerary culture of the period, the sort that reminds the living of their own mortality: "Sum quod eris, fueramque quod es," what I am you will be, what you were I once was. Also recorded was a gate inscription from 1693, commissioned by one Johannes Murray of Aberdeen, carved by Johannes Sinclair, and bearing the words "Sursum Cor" and "Memento Mori." A separate stone nearby noted that John Ford, then Mayor of Limerick, had repaired the churchyard walls at his own expense following the siege, presumably the Williamite siege of the 1690s.

The church sits on the north side of John's Square and is closely associated with the former John's Gate and the adjacent town walls, with the Citadel nearby and St John's Hospital incorporating part of the wider site. The Catholic Cathedral of St John's is visible to the east. Visitors approaching from John Street will find the west elevation with its Romanesque portal and blind arcade of round arches facing the square. The boundary wall has seen alterations over time, and the historic east wall was recently demolished. The oculus windows set into the clerestorey bays are worth a close look, as is the cornice detail on the spire. The monument to Thomas Power and its twelve apostles are long gone, cleared away in the 1763 works, but the 1827 account of them, preserved in Fitzgerald's survey, gives a clear enough picture of what was lost.