The parish church stands on the site of the wooden church built by St. Aidan in 635 AD, which during the Anglo-Saxon period was replaced by a small stone church. The Benedictine monks of Durham, who in the 12th century began to build the second monastery, decided this should be the parish church and employed and paid a chaplain to care for the villagers.

The building was enlarged twice: once in the 12th century by a Romanesque north arcade and a Norman apse (now gone) and an early English south arcade and chancel in the 13th century. Parts of the original Saxon church survive in the wall containing the chancel arch. The tower and the porch were added later.

More information can be found here
http://www.stmarysholyisland.org.uk/tour.htm