The chancel, where the altar would once have stood, is entirely gone; what survives is a single arch of pointed segmental form, rising in isolation to mark where the nave ended and the sacred space began. It is the kind of detail that rewards a slow look, a structural full stop with nothing left on the other side of the sentence.

The church was dedicated to St Nicholas and is thought to have fallen into disuse and ruin sometime around the mid-seventeenth century, a period of considerable disruption to ecclesiastical life in Ireland. The surviving nave is a plain, rectangular structure, built of random rubble masonry and aligned east to west in the traditional manner. Its internal dimensions are modest, roughly ten metres long and just over five metres wide, with walls nearly a metre thick. Light would have entered through narrow slit openings in the south wall, and a tall round-arched window sits at loft level in the west gable, which also carries a double bellcote, a small projecting structure designed to hold two bells. Facing doorways with pointed segmental arches sit opposite each other at the west end of the nave, a relatively unusual arrangement that hints at the building's former use as a thoroughfare for processions or community gatherings. To the northeast, positioned on the footprint of the vanished chancel, is the tomb of Austin Cooper.

Kinsaley sits close to the M1 corridor north of Dublin airport, which makes the quietness of the site something of a mild surprise. The ruin stands in what was the old parish, now largely absorbed into suburban north Dublin. Visitors should look carefully at the surviving chancel arch, which gives the clearest sense of the building's original two-part structure, and note the contrast between the rough rubble walls and the more carefully worked stonework of the doorways and window. The double bellcote in the west gable is worth examining closely, as such features are not especially common on modest rural churches of this type.