Towards the end of the fourteenth century, the nave walls of this parish church on the summit of a broad hill outside Bannow were fitted with crenellations and wall-walks, the battlements you might expect to find on a castle rather than a place of worship. Eight pairs of large beam-holes in the north and south walls, still visible today, supported not only the roof but possibly an upper room as well, suggesting the building was designed to function as a refuge or strongpoint. The west gable once carried a bell-cote, but that had already collapsed by around 1830, and the top of the south nave wall was conserved as recently as 2020, deliberately without restoring the crenellations.

The church was probably founded before 1200, most likely by monks from Canterbury, and it passed to Tintern Abbey in County Wexford in 1245. Tintern, a Cistercian house, still held 120 acres and the rectory here when it was suppressed in 1538. By 1615, when Thomas Ram, the Protestant bishop of Ferns, carried out a visitation, the church was still technically impropriate to Tintern, meaning its revenues were held by that institution rather than the parish; John Harris was recorded as vicar, and both the church and chancel were reported to be in repair. The chancel arch, a round opening of dressed voussoirs nearly four metres high, survives intact, and corbels on its western face hint at a rood screen, the wooden partition that would once have separated nave from chancel in a medieval church. The pointed east window, around four metres tall, retains fragments of tracery from what was a three or four-light opening; its stonework is Dundry, the distinctive oolitic limestone quarried near Bristol and frequently imported to south-east Ireland in the medieval period, and one stone carries a mason's mark. A bullaun stone, a rounded boulder with a deliberate cup-shaped hollow of uncertain but probably ancient ritual use, sits just inside the south doorway. At the south-east angle of the nave lie two graveslabs and a sandstone sarcophagus; one slab carries carved heads of a man and a woman and a partly legible inscription commemorating Joanes Colfer and a woman named Anne, with a surname rendered variously as Lusgin or Siggin.

The church's most decorated surviving artefact is no longer on site. A complete Romanesque font, probably carved from Dundry stone and showing Anglo-Saxon stylistic influence in its banded decoration, was removed at some point and is now kept in the Roman Catholic church at Carrick-on-Bannow, where it survives intact but painted white. The site of Bannow Castle lies roughly seventy metres to the south-east of the church, and a holy well known as Lady's Well is about 190 metres to the east.