The church of St Cybi, Holyhead, was refered to as a clas, a Welsh monastic community, in 1282 and was later a college of a provost and twelve cannons. The college was disolved in 1548, since when the church has been parochial.

The present building consists of a short aisled nave of three bays, crossing with trancepts, a long chancel and south chapel, west tower and south porch. The long thirteenth century chancel is the earliest part. The trancepts, aisles and porch were added between about 1480 and 1520. The west tower is seventeenth century and the south chapel was added in 1896-7. The nave, aisles, transepts and porch have splendid crenelated parapets with pinnacles. The tower has two tall plain stages and a low pyramidal roof or spire. The fine sixteenth century south doorway has a plethora of heraldry and beasts, and the wall above is lined with flowing tracery around a relief-carved figure. At the sides are canopied niches without their statues.

The church stands within the walls of what is thought to be a Roman stronghold (NPRN 15607). The eastern towers, overlooking the harbour, are thought to have been rebuilt in the medieval period and the enclosure may have served as a fortified precinct. The nave of a smaller church, Eglwys-y-Bedd (NPRN 43590) stands in the southern part of the enclosure. The present building is fourteenth century, but it is thought to have replaced an earlier structure.

Inside, the monument to W.O. Stanley, of 1884, is an exceptional piece of Late Victorian sculpture by Hamo Thornycroft, who was passed the commission originally offered to G. F. Watts. Seen through a bronze arabesque screen, a white marble effigy on an Italian Renaissance chest is set against a dark eastern wall between two angels with dramatically spread wings, offering a wreath and a torch.

Remains of frescoes have been found in the interior, including a Tudor rose in a border, and Royal Arms boards from 1817 that superceded an earlier framed Hanoverian arms in the north aisle. There is also a reused armorial pew front.

The site of Ffynnon Cybi, St Cybi's well (NPRN 32171) lies 112m to the north-north-west.

Sources include:
RCAHM Anglesey Inventory (1937), 28-31
Haslam, Orbach and Voelcker (2009), The Buildings of Wales: Gwynedd. Pevsner Architectural Guide, page 129.
Richard Suggett, Painted Temples: Wallpaintings and Rood-screens in Welsh Churches, 1200–1800, (RCAHMW 2021), pp. 19, 226.

RCAHMW 2021