Altered, re-roofed, re-floored, and repeatedly renovated across eight centuries, it retains, in the words of architectural historian Harold Leask, its original extent and plan, a continuity that most churches of comparable age in Ireland cannot claim.

The earliest dateable fabric goes back to the thirteenth century, identified partly through a single transitional pointed window-head, a style belonging to the period when Irish builders were moving from the rounded Romanesque arch towards the fully Gothic pointed form, and partly through a group of three lancet windows in the west wall, thought to belong to the middle of that same century. The chancel arch survived until 1730, when it was taken down, and the building was substantially altered again in 1759 to 1760, with major works following in 1835 to 1837 and again in 1856 to 1858. During that last campaign, the re-flooring of the nave turned up a number of stone coffins constructed from flat flags laid parallel with one another, capped by thin covering slabs. The burials were believed to be those of clerics, based on ornaments found alongside some of them. On the south side of the nave, fragmentary remains survive of a sixteenth-century structure known as the Galway Chapel. Inside, the church holds a rectangular font with a spiral shaft, a carved statue of a cleric carrying a pastoral staff set into a niche above the west door, and a substantial accumulation of grave slabs, memorials, and wall plaques ranging from the sixteenth to the eighteenth century. Among these are tombstones of Jacobus Galwey, dated 1627, and William Galwey, dated 1628, as well as a monument to Robert and Helena Southwell, dated 1679, which features what has been described as an unusual sarcophagus surmounted by an urn, and a separate memorial to Katherine Percival, dated 1682.