St Mary's church was a parish church during the medieval period, belonging to the Deanery of Sub-Aeron. It was also the priory church for the medieval Benedictine cell of Chertsey Abbey, whose conventual buildings are thought to have occupied the adjacent site of the current Cardigan and District Hospital. At the dissolution, priory and church fell to the Crown. The church continued as a parish church. The priory buildings were granted to Bisham Abbey, then to William Cavendish, when they became a private residence.

The church, a Grade II* listed building, consists of three-bayed chancel, five-bayed nave, south porch, three-storeyed west tower, two-bayed vestry (north of the chancel east bays) and transeptal organ chamber (north of chancel west bay). It is constructed of local slate rubble. The chancel, the monastic priory church, dates from the fourteenth century and is described as being of exceptional quality. Its blocked south door is thought is thought to have been associated with the former priory buildings. The piscina, in late Decorated style, is contemporary. The octagonal font bowl with quaterfoil mouldings is thought to be medieval in date. One of the east windows contains fragments of fifteenth-century glass, which are the sole survivors of the medieval stained glass moved to Hafod (NPRN 5577) by Thomas Johnes (and subsequently burnt in Hafod's fire of 1807). The Perpendicular chancel windows were inserted in the early sixteenth century.  A wall painting of Our Lady of the Taper was destroyed at the Reformation.  

The porch was rebuilt in 1639. The nave was partially rebuilt in 1703. The tower collapsed in 1705, was partially rebuilt in 1711 and completed in 1748. This rebuild may be a copy of the original tower. A wall painting of a salutary inscription relating to theft from a poor box dating to 1742-3 has been recorded (but is now lost).  A clock mechanism dated 1759 is lying loose in the church. The eastern half of the nave north wall may have been rebuilt in 1798. Buttresses and pinacles are thought to have been rebuilt in the eighteenth cenrury. The east window of the nave south wall was rebuilt in 1847. Alterations were undertaken in 1855 when the church was reseated. The vestry and organ chamber were added in the late nineteenth century (both present by 1888). The was some restoration in 1904-1906, by L. Lewis, Cardigan. The chancel was restored in 1923, to the designs of W.D. Caroe, Westminster. The pews and tower screen are thought to date from this time, and wall-paintings including a decalogue and other texts were removed from the chancel to the tower in 1924. In the later twentieth century the vestry east bay was converted into a boilerhouse.

Sources include:
Cadw, Listed Buildings Database
Cambria Archaeology, 2000, Ceredigion Churches, gazetteer, 48
Richard Suggett, Painted Temples: Wallpaintings and Rood-screens in Welsh Churches, 1200–1800, (RCAHMW 2021), pp. 19, 22, 128.

RCAHMW 2021