St Mael and St Sulien's Church is located in the centre of Corwen. It is situated within a curvilinear churchyard, almost entirely bounded by buildings, with a road delineating its north and east sides. A stream borders the east side of the churchyard. Historic documents refer to the church as St Sulien's, as does first edition (1875) Ordnance Survey mapping. The church appears to have has a change of name before 1901, as it is depicted as St Mael and St Sulien on second edition (1901) Ordnance Survey mapping.

A prehistoric stone, known as Garreg i big yn y fach rewllyd (the pointed stone in the frozen nook) has been built into the external wall of the north porch. Local tradition states that every attempt to erect a church on a different site failed, and the founders were directed by a supernatural power to the site where this stone stood. A seventh to ninth century cross inscribed stone is now a lintel for the south vestry door. The church is thought to have been an early medieval mother church. It was first mentioned in documents of 1222, and the fact that the church was noted to have sixteen clerics signifies its continuing importance at that time.

An early medieval pillar stone, inscribed with a linear Latin cross, has been reset within the church. A cross shaft and base (NPRN 306609), thought to be twelfth century in date, is located immediately south-west of the church. The top of the shaft is carved with interlace ornament and there is a small latin cross in relief on its east face. Fragments of two stones decorated with plaitwork and interlace were located in the church at the beginning of the twentieth century, but have since disappeared. They are thought not to have derived from the shaft and base, as they were probably of a different geological composition. A medieval effigy slab, inscribed in Latin, is thought to date to the fifteenth century. It commemorates Iorwerth Sulien, vicar of Corwen. A triple stepped plinth on the north side of the lych gate has a sundial with gnomon dated 1992, which replaced a carved wooden pillar supporting a sundial dated 1715. The lych gate dates to 1886.

The building was originally cruciform in plan, consisting of nave, chancel and north and south transepts. The present church is a Grade II listed building and is orientated south-west to north-east (although ecclesiastical east will be used in this description of the building). It is constructed of rubble stone and consists of a long nave and chancel, south aisle shorter than the nave, west tower attached to the nave, north porch, and two south vestries. The circular font is twelfth century. The west tower is medieval. Three medieval lancet windows remain in the east wall, although they have been reset. The roof of the north transept may be late medieval. The nave roof dates to the seventeenth century. In 1730 the building was noted to be a large church consisting of nave and chancel, west tower and two transepts, each lit by four large lancets. The north wall had a single window and the south wall three windows, one of which was recent. At that time the walls of the north transept were noted to be bulging and unstable, the floor was roughly flagged, and the Creed, Lord's Prayer and Ten Commandments were written on the walls. The north porch was added in 1777, and the north transept was repaired. A plaster ceiling, new bells and new windows were also added. The north transept functioned as a school prior to 1845. The building was restored in 1871, and the south transept was removed, with a south aisle added. The vestry was added in 1898. The tower was restored in 1907, when the top stage was repaired, windows were reset onto new sills and new louvres were inserted. A heating chamber underneath the tower was also excavated, and graves were found. In 1984 the church was struck by lightning, which consequently resulted in the replacement of the chancel ceiling.

The church ones featured a blackletter verse, or englynion, which was noted around 1698, but is now lost.

Sources include:
Beverley Smith, J, Beverley Smith, Ll, 2001, History of Merioneth II, 335-337
Clwyd-Powys Archaeological Trust, 2000, Historic churches of Denbighshire and the Vale of Clwyd: gazetteer, 312
Ordnance Survey, 1875, first edition 25inch
Ordnance Survey, 1901, second edition 25inch
Richard Suggett, Painted Temples: Wallpaintings and Rood-screens in Welsh Churches, 1200–1800, (RCAHMW 2021), pp. 248–50.

RCAHMW 2021