The first documentary reference to St Bueno's dates to 1254. It is situated within a 'D' shaped churchyard, whose boundary was probably originally curvilinear. Its north and west boundaries are currently staright, but a possible former boundary can be traced as a very low curving scarp in the field to the west. The parish of Gwyddelwern now contains the former parish of Llanaelhaern.

The church is a grade 2 listed building, the medieval fabric of which consists of rubble stone with occasional boulder stones. The Victorian fabric consists of small or medium sized grey shale blocks, with pink sandstone blocks. It consists of nave with slightly narrower chancel and south porch with a tower and spire above. The octagonal font is medieval, and fragments of medieval stained glass, formerly from the east window, are now in the north window of the chancel. Parts of the late medieval roodscreen are incorporated into the current screen, including six tracery heads near the base. The eastern pair of chancel windows and small priest's door are thought to be fourteenth century in date. In 1538 it was noted that the induction of a new vicar took place in a newly erected church. Several wallpaintings and inscriptions were noted in 1729, but they were described as ‘poor’. They were repainted in 1745 by Thomas Davies, painter, according to a lost inscription in the chancel. In 1730 the church was described as having one aisle, whose measurements were given as thirty yards by nine yards. A west gallery was noted, with the nave being lit by two windows on each side and another for the gallery. The chancel was lit by one window on each side and another large east window. A north and south door were noted, in addition to a chancel door. The floor was constructed of very rough flags. Parts of the medieval roodscreen are now incorporated into the western gallery and pews before 1849. Before 1880 the building had a west bellecote with two bells and a south porch. The building was restored in 1880, and the south porch replaced, with a tower and spire built above it. The chancel was also rebuilt. A pulpit was added, its pinnacled buttresses taken from the rood loft parapet which had served as the front of the west gallery.

Sources include:
Beverley Smith, J, Beverley Smith, 2001, History of Merioneth II, 338-340
Clwyd-Powys Archaeological Trust, 1999, Historic churches of Gwynedd: gazetteer, 276
Richard Suggett, Painted Temples: Wallpaintings and Rood-screens in Welsh Churches, 1200–1800, (RCAHMW 2021)

RCAHMW 2021