The church is ruined and roofless and consists of a nave and chancel separated by a solid wall. The nave measures c.9.9 m x 7.16 m, the chancel 13.64 m x 7.19 m. The N and E walls of the nave and most of the W wall are still intact, while only the E part of the S wall remains. The walls are of rubble. There are plain round-headed windows with an interior splay towards the E end of the N and S walls, and a damaged round-headed window in the E wall of the nave, set slightly S of centre. The chancel, which is longer than the nave, was evidently added at a later date. The N and E walls remain, as well as the lower courses of the S wall. The E wall has a 13thc. double window with pointed arches and small sculptures on the central mullion with a plaited motif and a male head. Some sculptures have been reset on top of the S wall in the centre. The lower part of a reconstructed round tower remains near the NW corner of the church.

A monastery was founded here by St Finian the Leper in the 7thc. A stone church is mentioned in 1061, and the arrival of the Normans is recorded in 1177 (AI). The ‘great’ church was damaged by gales in 1282, and its holy cross was broken (AI). The record of this event also mentions that the church had been finished 1158 by Amhlaoibh, son of Aongus O Donnchadha (Book of Mac Carthy, 1158, 6). The death of Aongus is mentioned in same year, adding that Amblaoibh was buried on the right side of church at Aghadoe 'which he himself had built in honour of the Trinity and Mary' (Book of Mac Carthy, 1158, 7).

The doorway has been inaccurately rebuilt at some point in its history. In structural terms it can be compared to doorways at Freshford (Kilkenny) and Clonkeen (Limerick) both of which have a plain, continuous inner order and slots on the soffit, close to the springing of the arch for centuring. Rynne (NMAJ, 1987) suggests that this may originally have held a wooden tympanum, which would have measured h. 0.45 m x w. 0.88 m x d. 0.08 m. The capitals find close parallels at Clonkeen, on the chancel arch of St Caiman’s Inishcealtra (Clare) and with the bases at Freshford. Parallels for the foliate carving are particularly striking in the N window surround at Temple na Hoe, Ardfert. The reference to the construction of the ‘great’ church at Aghadoe in 1158 provides a rare case of an independently-dated Romanesque church. If the current ‘cathedral’ is this building (and this has not been proven), then it provides an important chronological point of reference for a series of related Munster and south Leinster churches. The label was probably originally decorated with a series of bosses as at Temple na Hoe, Ardfert. The bosses on the first (from N) label stone are faceted as at Temple na Hoe.