The church consists of a nave measuring 17.25 m x 6.8 m internally and a chancel 5.76 m in length. A later range of conventual buildings lies S of the E end of the nave. The N wall of the nave collapsed in the 15thc. and was rebuilt further S, in line with the N wall of the chancel. There is a doorway near the W end of the N wall of the nave and two doorways near the E end of the S wall of the nave, one leading into the sacristy, the other to the exterior. (Leask’s plan also shows a W doorway). There is a doorway near the W end of the N wall of the nave and two doorways near the E end of the S wall of the nave, one leading into the sacristy, the other to the exterior. (Leask’s plan also shows a W doorway).

A monastery was founded in the 7thc. by St. Colman mac Duagh. The Augustinian abbey was built to replace the early monastery, which was ruined in the early 13thc. by William Fitz Adelm de Burgo. Archdall, Brash, and Fahey attribute the foundation to Bp. Maurice Ileyan (1254-84). Leask, based on architectural evidence and on the traditional association with Owen O’Heyne (d.1253), suggests a date in the second quarter of the 13thc., and proposes that Bp. Maurice may have built the E range of the conventual buildings. The N wall of the church was rebuilt after a partial collapse in the 14thc. or 15thc.

The sculpture is characteristic of the 'School of the West'. The exterior angle shafts are found on earlier Romanesque buildings, for example at Monaincha, Temple na Hoe at Ardfert, Tuamgraney and Rathblathmaic. The continuous window mouldings are similar to examples at Inishmaine and Temple Melaghlin, Clonmacnoise, and the arrangement of two framed lights linked by a gable on the exterior of the E window is similar to the E window of Clonfert Cathedral (Galway). The keeled and chamfered mouldings at Kilmacduagh however suggest a somewhat later date than Clonfert. The chancel arch capitals are more complex and three-dimensional than those of the E window, and comparisons for the foliage designs can be made with the capitals and corbels at Corcomroe and Killaloe Cathedral (Clare). Leask (1960, 35) compared the foliage on one of the chancel arch capitals to an example at Monasteranenagh (Limerick), but there are closer comparisons for this inverted lily motif at Killaloe Cathedral (S tower arch, E corbel; chancel N side, corbel 2). The iconography of fighting beasts or dragons can be compared to examples at Boyle (Roscommon), Ballintober and Inishmaine (Mayo), and Drumacoo (Galway); the tear-drop shape of the eyes is similar to the dragon on a capital of the doorway at Drumacoo (E jamb, first order). Kalkreuter compares the dragon heads to those at Boyle and Drumacoo, and the interlocking necks to those at Ballintober; she suggests that the biting dragons at Kilmacduagh may have been influenced by a late Romanesque panel in Clonfert Cathedral carved with two fighting beasts. Based on stylistic analysis, Leask suggested a date sometime in the second quarter of the 13thc., before the death of Owen O’Heyne in 1253. Harbison favours an earlier date, based on his dating of the Clonfert panel to 'probably within the second decade of the 13th century' and the generally-held assumption that Kilmacduagh is a later work by the same mason. Kalkreuter considers the work to be by the same masons as Corcomroe and Drumacoo and proposes ‘a date between the temporary cessation of building activity in Corcomroe in 1227 or 1228 and the work on the south porch in Drumacoo around 1235’. A date in the late1220s - mid1230s seems most likely on the basis of style.