The oldest part of the church is to the south, with the north aisle added later – and an especially good example of nave-arcading with four handsome pointed stone arches of the Doric Order.  The church was used for centuries as a mausoleum by the Ulster-Scots Montgomery's and their successors as landlords, the Stewarts (Viscounts Londonderry).

Last used for public worship in 1817 when the new St Mark’s Parish Church was opened, the church served as a courthouse in its latter days.  Its walls are carefully preserved and enclose gothic archways, pillars, enormous tombs and memorials.  

One reliable mid-19th century source reported that a former minister of the Priory returned one night with a horse and cart and dug up a lot of bones of the people who were buried here, taking them to his farm at Moneyreagh and using them as fertiliser on his potatoes...