It was built during the latter stages of the Nine Years' War in June 1601 by Lord Mountjoy to help secure Moyry Pass and the Gap of the North.
Moyry Castle is a State Care Historic Monument sited in the townland of Carrickbroad, in Newry, Mourne and Down District Council area, at grid ref: J0576 1466.
In the patent rolls in 1606 King James I set aside the following area for the maintenance and security of the castle, fort and ward of Moyry: the towns, Dromintee, Carrickbroad, Dromad, Faughilotra, Faughart Faughiletra, part of Feede.
It was Mountjoy's belief that "in every fort some little keepe (or tower) of stone be built, neither need these little castles be works of any great charge for they may be easily made such as this people will hardly force them".
In 1641 the confederates garrisoned the castle and in August–September 1690 King William's army, under the command of Schomberg marched from Belfast, through this pass to Dundalk on their way to the Boyne.
There were casualties on both sides, and Dempsey, a veteran of almost half a century of European warfare died of his wounds on the eve of the Battle of the Boyne at Oldbridge.