It is an active Anglican parish church in the deanery of Llanfyllin, the archdeaconry of Montgomery, and the diocese of St Asaph,[1] and is designated by Cadw as a Grade II* listed building.

[4] It shares it name with the church in the village of St Harmon in Radnorshire (Powys), where the diarist Francis Kilvert was a curate.

The earliest documentary evidence relating to the church is in the Norwich Taxation of 1254 and its fabric dates from around this time.

Work was done on the church in 1852 but a larger restoration was carried out in 1859 under R. K. Penson when the vestry on the west wall was replaced by a new one on the north side.

Changes were made to the gallery, the west gable was rebuilt, round-headed windows were inserted in the nave and the chancel, and a spire was added to the belfry.

[3] The church is built in shale with sandstone dressings, and a red tile roof.

Its plan consists of a nave and chancel with six bays in a single chamber, a vestry on the north near the west corner and a porch opposite it.