St Mary's church was located on the east-facing slope of the Garw Valley above what was then, in the late nineteenth century, the hamlet of Pontyrhyl. It was built in 1891-2 to designs of architects E.H.Bruton and E.J.Williams of Cardiff, in the English Gothic style, as a chapel of ease to St Theodore, Pontycymmer.
The building consists of nave and continuous chancel divided internally by a timber screen which was continuous on (liturgical) north and south of the chancel, behind choir stalls, to form a vestry and organ chamber. The sanctuary was marked off from the rest of the chancel by a lofty arch on the same line as the altar rail. The porch was on the (liturgical) south side. The church closed in 1986 though the building is still extant.
When first built, there was a small 'Mission Room' nearby at SS90498954 portrayed on the Ordnance Survey second-edition map of 1899. It had gone by the third edition of 1918.

Sources:
churchplansonline.org
http://www.cofiadurcahcymru.org.uk/arch/query/page.php?prn=GGAT00927m
OS County Series 25-inch map: Glamorgan sheet XXVI.15

David Leighton, RCAHMW, 13 January 2015