This tranquil location on the eastern tip of Anglesey has remains spanning over 1,000 years. It was the site of a monastery dating back to the time of St. Seiriol, who is believed to have lived in about the 6th century. A holy well which survives may have its origins in this period. In the early 13th century the Celtic community was reorganized under the Augustinian Rule, and at this time the priory church was enlarged. This now serves as the parish church.
The monastery at Penmon is reputed to have been founded by St Seiriol, a 6th-century holyman and friend of St Cybi. The monastery prospered and in the 10th century fine crosses were set up at its gates, but the Viking raids have destroyed all other evidence of this date. During the 12th century, revival under Gruffydd ap Cynan and Owain Gwynedd the abbey church was rebuilt, and it remains the finest and most complete example of a church of this period in Gwynedd. In the 13th century the Celtic monasteries were persuaded by Llywelyn ap Iorwerth to adopt a more regular rule, and Penmon eventually became an Augustinian priory with quite substantial conventual buildings. The priory survived the Edwardian conquest and expanded slightly, but was dissolved in 1538. The buildings passed into the hands of the Bulkeleys of Beaumaris, who enclosed much of the land as a deep park and built a fine dovecote. They also converted the prior's lodging into a rather attractive house. Throughout this time the priory church remained in use, as it does today