It follows the architectural style of a Loire Valley château, being redesigned by the architect Sir Charles Lanyon in the mid-19th century.

The castle hosts occasional concerts; performers have included Van Morrison, Glen Hansard and Bap Kennedy.

Killyleagh was settled in the late 12th century by Norman knight Sir John de Courcy, who built fortifications on the site of the castle in 1180 as part of a series of fortifications around Strangford Lough, which he had built in order to protect the lands he had seized from the native Irish.

In 1602, Gaelic chieftain Con O'Neill of Clandeboye owned large tracts of North Down, including Killyleagh.

He supported the Stuart monarch Charles I of England and the castle was besieged in 1649 by Oliver Cromwell's forces[2] who sailed gunboats into Strangford Lough and blew up the gatehouse.

He erected the north tower and built (or perhaps restored) the long fortified bawn (wall) in the front of the castle.

Gawn's great-grandson, Archibald Hamilton Rowan, an Irish nationalist of the United Irishmen, lived in the castle as one of his homes between 1806 and 1834 after his return from exile in America.

Hamilton Rowan's grandson, Archibald Rowan-Hamilton, and his wife employed architect and engineer Sir Charles Lanyon from 1850 to renovate the castle,[2][4][7] creating its romantic silhouette with the addition of the turrets.

Gawn Rowan Hamilton has said: "I have a cutting from the Belfast Telegraph which tells the story of my great-great uncle being woken at 2 am and exchanging gunfire from the battlements, which was terribly exciting.

Benjamin Ferrey created a baronial gatehouse to match the two surviving corner towers to the castle.