The church has an undivided nave and chancel, with the E end raised approx. 0.9 m over a vaulted crypt. The E wall has two round-headed windows traversed by a wall-passage and is 11.2 m wide; the church is narrower at the W end. In the 15thc. the present W wall was built, shortening the church, which was originally 39.32 m long, to 26.36 m on the N and 26.82 m on the S side. The N wall was restored and domestic buildings added to the S. The S wall of nave is no longer standing, apart from a partially rebuilt late medieval doorway at W end.

The convent was probably foundedc.1189/90 by Domnall Mór O'Briain for Augustinian canonesses (Ware). Built on the lands of Clare Abbey, which was founded at the same time for regular canons (Gwynn and Hadcock). Abbess Slaine, daughter of Donnchad Cairbreach O'Briain, d.1259 (Gleeson). The abbey was in ruins in 1617.

The crypt under the choir is an unusual feature in Ireland, and results from the steep fall of the land at the E end towards the lake. The wall-passage in the E wall is also unusual, but can be parallelled at Kilfenora Cathedral, where there is a wall passage in the W wall, and at Killaloe Cathedral, which has a wall-passage in the transept. The decoration of the E window is Transitional in style, belonging to the 'School of the West'. There is similar chevron on the S doorway at Drumacoo and the E window of Temple Jarlaith, Tuam. The continuation of the abacus as a string course across the window splays is similar to the E windows of O'Heyne's church at Kilmacduagh. Leask dated the work certainly 'to a very late stage in the Transition, hardly earlier - and quite possibly later - thanc.1225'. A date in the late 1220s to mid-1230s seems likely on the basis of style.