What makes this place quietly anomalous is not simply its age or its setting, but the distance between its official suppression and its actual end. Long after the Crown had nominally disposed of it, the friars appear to have carried on here, sheltered by the remoteness of the site and by well-connected local allies, well into the eighteenth century.

The friary was founded in 1456, when Hugh O'Malley, a friar from the Observant Augustinian house at Banada in Co. Sligo, obtained papal permission to build at the place then called Leithearmursge. The land was granted by Tadhg mac Diarmaid Ó Máille, who ruled Umaill at the time and died in 1467; the O'Malleys were a seafaring family who controlled most of what is now the barony of Murrisk. A later document from 1656 names Lady Maeve O'Connor, wife of Diarmuid Bacach O'Malley, as the founder, and the apparent contradiction is not unusual: mendicant friaries, those of the begging orders who relied on lay donations rather than endowments, were typically built in stages and funded by several benefactors over time. The papal permission itself explains why a friary was thought necessary here at all: the place was, in its own words, far remote from cities, towns, and castles, and the inhabitants had not hitherto been instructed in the faith. The friary was dedicated to St Patrick, and relics associated with the saint, including the shrine known as Fiacail Phadraig (St Patrick's tooth), now in the National Museum of Ireland, and St Patrick's Black Bell, later acquired by the Royal Irish Academy, are believed to have been kept in the church. It also served as the traditional starting point for the pilgrimage climb to Croagh Patrick's summit. After the Dissolution of the Monasteries, a 1574 report to the Lord Deputy noted the place was possessed either by friars or rebels, and in 1578 the property was granted to James Garvey, brother of the Protestant Archbishop of Armagh. The community, however, was not so easily removed. Two chalices commissioned for the monastery in the seventeenth century confirm its continued life: the Viscount Mayo Chalice of 1635, made for Maeve O'Conor in memory of her husband Theobald Burke, and the Murrisk Chalice of 1648, commissioned by the Augustinian friar John de Burgh and made in Galway by Richard Joyce.

The surviving fabric rewards close attention. The walls, built mostly of roughly coursed dressed limestone, are L-shaped in plan, with a nave and chancel church running east to west and a range of domestic buildings projecting north from the east end. The bell tower at the west end is collapsed but unusual, since in mendicant churches the tower was conventionally placed between nave and chancel rather than at the far end. The east gable retains a five-light window with switchline tracery and trefoil heads that one architectural historian, Harold Leask, writing in 1943, judged perhaps the best window of its type in the west of Ireland. The high altar remains in place beneath it. Small carved stone heads survive on the external walls near the chancel windows. The cloister, specified in the original papal permission, has left no trace above ground, though corbels and a string course suggest a covered walkway once existed, possibly timber-framed rather than a stone arcade. In the east range, the barrel-vaulted sacristy and the probable chapter room are both largely intact.