A roofless nave and chancel church, with walls and gables intact. The upper parts of the N and S walls were probably restored in the 16thc. The elaborately carved W portal was surmounted by a tangent gable. The N wall of the nave has a round-headed window in the centre and a square window of rougher masonry towards the E end. The S wall has two round-headed windows. The chancel arch leads into a small rectangular chancel, originally vaulted and two-storied, with a plain square opening in the gable above the chancel arch. In the N wall of the chancel is a square opening with the sill c. 0.3m from the ground (a later door opening?). Two round-headed windows in the E gable lit the upper and lower storeys of the chancel. Sandstone is used for quoins, windows and door openings, otherwise the building is of uncoursed limestone. The dimensions of the nave are 12.03m x 7.23m, those of the chancel are 3.65 m x 2.6 m. The loose sculpture and some moulded fragments that were recorded in 1994 were no longer on the site in 2002.

A monastery was founded at this site by St Farannan in the 10thc. At the synod of Rathbreasil (1111), Donaghmore was merged in the diocese of Lismore and its lands became the property of the See. The church was vested in the care of the Board of Works in 1883, at which time conservation works were carried out by Thomas Deane.

Although badly damaged, the doorway and chancel arch provide evidence of a rich decorative program. The tangent gable may be compared to other examples of this feature at Roscrea (Tipperary), Freshford (Kilkenny), Killeshin (Laois), Clonfert (Galway), and the round tower at Kildare. The porch appears to have projected, as at Freshford, rather than having a flat tangent gable. The rich decoration of the arch and jambs with a combination of beaded bands, chevron and foliage ornament suggests a date in the last third of the 12thc. The foliage motif with alternating facing groups of triple leaves on the jambs also occurs at Clonfert; the beaded chevron with low-relief foliage in the triangles is similar to that on the E window of Annaghdown Cathedral (Galway), and is also found on a fragment at nearby St Patrickswell (Tipperary). The capitals of the chancel arch are similar in design to examples at Clonkeen (Limerick) and St Caimin's Inishcaltra (Clare), but the foliage decoration at Donaghmore is more elaborate. The jamb stone with a biting beast head is similar to those on the chancel arch of Temple Finghin, Clonmacnoise, but is carved in lower relief. Burke (1896) gives a reconstruction of the W doorway with a tympanum; this is an unusual feature in Irish Romanesque, found also at Cashel, Kilmalkedar, and Aghadoe.