These weathered stone walls, measuring 15.6m by 5.2m internally with a north transept of 6.6m by 5.15m, may have originally belonged to St. Catherine's friary, founded by MacSwiny Bannagh for the Franciscan Third Order Regular. The main body likely dates to the 15th century, whilst the transept appears to be a 16th century addition; later modifications including the south arched transept gable, window alterations and western porch probably date from the 17th and 18th centuries.

The church's history mirrors the turbulent religious politics of Ireland. After the establishment of the Borough of Killybegs in 1615, the building was converted for Protestant worship, and by 1622 it was described as 'newly re-edified and well repaired'. During the chaos of the Confederate Wars, the church was likely abandoned, possibly providing shelter for displaced friars from Donegal. Following repairs around 1654-56, it continued serving the Protestant community throughout the 18th century, with maps from 1778 still marking it as the parish church.

This ancient place of worship finally fell silent in 1829 when the new St. John's Church was constructed, leaving these evocative ruins standing within their graveyard setting. Today, visitors can still trace the different building phases in the stonework, though much of the inner wall faces remain covered in centuries-old plaster. The various window openings, some possibly secondary insertions, offer glimpses into how the building was adapted and modified to meet the changing needs of its congregations across the centuries.