St Mary's Church, St Fagans, consist of a nave, north aisle, chancel, south porch, west tower, and north vestry. The church was built in the twelfth century but greatly altered and renovated in the early fourteenth century in the Decorated style. It was built of local rubblestone, and later Victorian work largely matches this but with ashlar buttresses and bath stone dressings. Further renovation occurred in the fifteenth century when the porch was added and the church reroofed with Welsh slate. The tower was likely built in the seventeenth century (likely 1616) and heightened in 1730. The tower is square and tapering with a moulded plinth to the base, and a western door with a dripmould above which are paired trefoil headed windows. The belfry has paired arched windows on all sides, gargoyles at the corners, and is topped with a battlemented parapet. The church was restored in 1859-60 at the expense of Baroness Windsor when the north aisle and vestry were added. Inside, the church has revealed masonry features. The inner face of the southern doorway is Norman, while fourteenth-century features can be seen in the chancel windows, priest's door, the chancel arch, tower arch, and sedilia and piscina in the chancel. The sedilia are canopied with pointed arches with a trefoil second order between which are headstops and botanical designs in the spandrels. There is also a series of stained-glass windows from the 1860s by John Hardman.

A blackletter Lord’s Prayer was found in 1860.

Sources include:
Cadw site report
Richard Suggett, Painted Temples: Wallpaintings and Rood-screens in Welsh Churches, 1200–1800, (RCAHMW 2021)

RCAHMW 2022