Two of its three doorways are now blocked up. The interior was deliberately dark, lit by only two windows. A strange offset runs along the inside of the south wall, suggesting the wall was thickened at some point by building a new face against the old one, though when or why is not recorded. Fragments of what appears to be an ogee-headed window, a style associated with late medieval decorative stonework, have been placed inside one of the blocked doorways and on the ground beneath it, with no surviving record of where they originally belonged.

The church was first built in the late twelfth or early thirteenth century, making it a product of the broader wave of Romanesque and early Gothic construction that reshaped Irish ecclesiastical architecture in that period. The west doorway, just over a metre wide and two metres high with a slightly pointed arch and simple moulded surround, is consistent with early thirteenth-century workmanship. The building was subsequently used as a parish church and substantially altered over time. Inside, two aumbries survive, small recessed wall cupboards used to store liturgical vessels, one in the south wall and one in the north. Four early Christian cross-slabs are now mounted on the interior walls. The most elaborate survival is a carved altar at the east end, which formed part of an O'Brien family wall monument, the upper section of which is fixed to the south wall. The O'Briens were the dominant Gaelic dynasty of Munster, and their presence here in stone reflects both their territorial reach and their patronage of the church on this island in Lough Derg. Externally, a buttress against the north wall contains a pierced water channel, sometimes called a slop-stone, a functional detail that points to the practical realities of maintaining a working religious building across several centuries.