Mac Lochlainn survived an attempt by Ruaidrí Ua Conchobair to unseat him in 1159.
In 1166, to attempt to achieve a diplomatic settlement with his neighbours, Mac Lochlainn arranged a truce and took hostages from many of the families in Ulaid.
In return he had given a solemn oath to the Bishop of Armagh and many other notables for his good behaviour.
Mac Lochlainn's allies abandoned him almost at once, and he was reduced to a handful of followers.
With sixteen of these closest associates, he was killed and his death attributed to the vengeance of Saint Patrick.