St John's church is located in a high position on the east side of Church Street, on the east side of Machen village. It is surrounded by a churchyard from which the ground falls to the south towards the A468.
The church was built in 1854-5 to designs of W. G. & E. Habershon of London and Newport. The need for a new church in Upper Machen, to compliment St Michael's in Lower Machen (NPRN 307316), was due to the rapid rise in population caused by industrialisation. In 1854, the rector opened a subscription list and soon had over £1,000. £400 was donated by Edward Buller, proprietor of Machen Colliery. Interestingly, the list of subscribers included non-conformists who were subsequently involved in the church. Some services were undertaken in Welsh.
The church was built in mixed Early English and Geometric styles. It is constructed of coursed, rock-faced stone under steeply pitched slate roofs, and features string course, plinth, and stepped angle buttresses, corbelled eaves with foliate bosses, and raised copings. Its ground plan comprises nave, narrower chancel, large gabled porch on south, north lean-to vestry, and a steeple to the south-east angle of the nave. Windows are lancets, mainly paired. The short steeple is in three stages with angle buttresses to south and east, the spire rising above the top stage. The unusual position and polygonal shape of the spire recalls the medieval steeple at Lostwithiel (Cornwall).
Inside, the nave is undivided with a seven-bay roof, the east bay wider, its high hammer-beam roof supported on corbels. The chancel has a three-bay arched brace roof, the trusses supported on plain corbels. The stone pulpit is polygonal with blind arches, supported on a short octagonal pedestal. The internal focus on the pulpit owes something to the preaching churches of the eighteenth century, but may also have been influenced by non-conformist participation. The octagonal font has incised quatrefoils, on a stem composed of four columns, on a large octagonal plinth.
Repairs to the church were undertaken from 1860, the steep pitch of the roof causing problems with damp, and in 1952 the steeple was rebuilt.

Sources:
extracts from Cadw Listing description
http://www.jlb2011.co.uk/walespic/churches/machen1.htm (image)

RCAHMW, 2 January 2015