The structure was once the Leper House of St. Brigid, a medieval hospital dedicated to the care of people with leprosy, and it sits quietly south-east of the ruined church of St. Bigseach, sharing ground with a holy well, a motte, and the former site of a gallows. That combination alone gives the townland of Kilbixy an unusually dense and varied medieval character, most of which has received little attention.

The building's origins have been disputed. Earlier scholars attributed its foundation to the Anglo-Norman lord de Lacy, linking it to a nearby motte thought to date from 1192, but that association has been judged without foundation, and no mention of the hospital appears in the Register of Tristernagh, the priory whose records document local ecclesiastical grants from the medieval period through to the early fourteenth century. The earliest firm reference comes from April 1409, when Archbishop Fleming of Armagh issued a letter on behalf of the leper house, described in Latin as a domus seu casella, meaning a house or small dwelling, at Kylbyxy in the diocese of Meath. The letter urged the faithful across several named deaneries to donate to the house's proctor when he came collecting, and offered contributors an indulgence of forty days, a common medieval incentive for charitable giving. The hospital may have been suppressed around 1540, when Tristernagh Priory was dissolved, though it is not recorded in the priory extents from that time. By 1837, when the scholar and topographer John O'Donovan visited Kilbixy, the building was already a mere ruin, one item in a brief list he compiled alongside the castle site, the moat, and the site of the gallows. A 1656 Down Survey map of the parish shows a small tower to the south of the Kilbixy church, which appears to be the same structure.

The ruins themselves are substantial enough to read architecturally. The walls, averaging 1.3 metres in thickness, are built from roughly coursed mixed stone with a rubble core. The ground floor, now filled with rubble, appears to have been divided into two barrel-vaulted rooms running across the building's short axis; barrel vaulting is a continuous curved ceiling of stone or brick, common in medieval structures where fire resistance and load-bearing strength were priorities. A flat-lintelled doorway with an internal splay survives in the south-east wall, and the first floor retains a large rectangular window with a round rear arch in the north wall. The ivy covering, measured at sixty-eight to seventy-eight centimetres deep on three of the four walls, means that a good deal of the upper fabric remains effectively unexamined.