[3][5] The first church community was established in Aberffraw in the 7th century by St Beuno (a Welsh holy man who became the abbot of Clynnog Fawr, on the Llŷn Peninsula in Gwynedd).

[3] During this work, the rector Hugh Wynne Jones discovered a blocked 12th-century arch set into the west wall.

[5] It is thought by some writers to be the original chancel arch,[3][5] but it has also been suggested that it was the entrance to a tower at the west end, which was said in 1833 to have once existed.

[4] Aberffraw became the principal court of the Princes of Gwynedd in the early Middle Ages, and St Beuno's may have been used as a royal chapel.

[1] The church is built in Late Decorated style from rubble masonry dressed with sandstone, with rendering on the outside of the wall at the west end.

[3] St Beuno's is entered through the porch in the south-west corner of the nave, which leads to an inner doorway set in a pointed arch.

[4] The window at the eastern end of the south wall has three lights with tracery, set in a pointed arch frame with a plain hoodmould around it.

[3] A survey in 1937 by the Royal Commission on Ancient and Historical Monuments in Wales and Monmouthshire also noted a memorial to Hugh Wynne, who died in 1714: he was Chancellor of Bangor Cathedral and rector of Aberffraw and Trefdraeth.

[10] Cadw (the Welsh Government body responsible for the built heritage of Wales) notes that while St Beuno's is "largely of late Medieval character", it retains "significant elements of a much earlier building including an unusually fine 12th-century chancel arch.

[3] Writing in 1846, the clergyman and antiquarian Harry Longueville Jones said that "the whole edifice has been lately repaired, new-roofed, and in various respects altered, so that some of its original features are now scarcely to be conjectured.

He also said that the doorway (as he described the arch in the west wall) was "richly ornamented", and commented that it had been "most judiciously uncovered" during the 1840 repairs.

[12] In 1849, the writer Samuel Lewis described the church as an "ancient structure", and noted in particular its two "spacious parallel aisles".

[5] A 2009 guide to the buildings of the region says that the church, which it describes as a "wide rectangle", contains "some of the most significant Romanesque work on the island".