Founded by the Norman noble William de Lacy, circa 1100. A church was built on the site and consecrated in 1108. By 1118 a group of 40 English monks began work on a Augustian Priory, the first in Wales. In 1135 after persistent attacks by the native Welsh the monks were forced to retreat back to Gloucester. The de Lacy family continued the building which was finished in 1217.

The Priory became one of the great medieval buildings in Wales. Following Owain Glyndwr's rebellion against the English in the early 15th century to Priory seems to have been barely functioning. After 1538 the Priory was supressed by Henry VIII's Dissolution of the Monastries.

Llanthony is set in the beautiful Vale of Ewyas, about 14 miles north of Abergavenny.