Ua Cerbaill, Murchad (d. 1189), son of Donnchad and king of Airgialla (Oriel), belonged to the Uí Nadshluaig dynasty of Fernmag, which left its name on the barony of Farney, Co. Monaghan. His mother is not recorded, but he had a sister Ben-Mide (who married Cú Maige Ua Flainn, king of Uí Thuirtre) and possibly a brother, Muirchertach. He succeeded to the kingship in 1168 on the death of his father Donnchad Ua Cerbaill (qv). After the Anglo-Norman intervention in Leinster, Murchad lent support to Ruaidrí Ua Conchobair (qv) and Tigernán Ua Ruairc (qv) on hostings against the Leinstermen in 1169–70. He brought a contingent to the ill-fated siege of Dublin in September 1171; when the Irish were put to flight, he withdrew his troops, apparently in some disorder.
In the winter of 1171–2, Murchad was among the northern rulers who submitted to King Henry II (qv) at Dublin. Nonetheless, he maintained his independence at local level. In 1176 he supported the Cenél nÉogain king Máel-Sechlainn Mac Lochlainn in an offensive against the Anglo-Normans, which reached as far as Slane. The Anglo-Norman conquest from 1177 onwards of most of the Ulaid overkingdom by John de Courcy (qv) clearly posed a threat to Murchad. When de Courcy led an incursion into the present northern Co. Louth in 1178, Murchad went in pursuit. He overtook the raiders and defeated them; the Annals of Tigernach (Tigernach Ua Bráein (qv)) locate the battle at Newry, and include amongst his allies Mac Duinn Shlébe king of the Ulaid. Sustained pressure from the new earldom of Ulster, however, drove Murchad, in 1184, into alliance with the Anglo-Norman earl Hugh de Lacy (qv), ‘lord of the Gall of Ireland’, in a campaign in Co. Armagh against de Courcy.
Murchad died in 1189 in religious retirement at Mainistir Mór (Mellifont, Co. Louth), which his father had founded for the Cistercians. His immediate successor, Muirchertach, was captured by the English, blinded, and hanged in 1194. A distant kinsman Niall, from a parallel line of Uí Nadshluaig, strove to maintain a modus vivendi with de Courcy; despite inroads into his realm by the English, he maintained control of the Airghialla heartland, which lay mostly within Co. Monaghan. Descendants of Niall, now bearing the family name of Mac Mathgamna (MacMahon), later became rulers of Airghialla.