MacMurrough (Mac Murchada), Muirchertach (d. 1282), king of Leinster, had for much of his career good relations with the English, but the changed political conditions of the 1270s led him to reassert his dynasty's traditional power. Due to genealogical confusion his parentage is uncertain; his father may have been Domnall or Art MacMurrough. Nothing is known of his mother or of his early life, but clearly his dynasty enjoyed a privileged position within the English settlement of east Leinster as a result of their kinship to the Marshall family. Muirchertach and his brother Art were also close to their cousin and successor of the Marshalls, Roger Bigod, lord of the liberty of Carlow. Bigod, also earl of Norfolk and earl marshal of England, continued the Marshalls’ accommodating policies by recognising Muirchertach as the leader of the Irish of Carlow.
From 1269, however, the Irish of the Leinster mountains became more militant, probably because of worsening weather, poor harvests, and the insensitivity of the archbishop of Dublin. In addition the Welsh victories, a few score miles from the Leinster coast, may have encouraged disturbance. On the whole, it seems the outbreak of war owes more to these factors than to what is termed the ‘Gaelic resurgence’. Between 1269 and 1273 Muirchertach remained aloof from the war. Worryingly, his traditional vassals (particularly Gearóid O'Byrne (qv; see Murchod O'Byrne)) became more powerful. Thus Muirchertach's entry into the war (1274) was not because of a deteriorating relationship with Bigod. Rather, he desired to maintain his traditional position in east Leinster, which he could not do without assuming leadership of the war against the English. The scale of the English defeat at Glenmalure that year suggests Muirchertach's impact was immediate, and that his leadership of east Leinster was intact. This is supported by the fact that his victory occurred some thirty miles outside Uí Cheinnselaig. Significantly, however, it was not outside his dynasty's traditional territorial ambit.
Unfortunately for Muirchertach, he was captured at Norragh by Walter L'Enfaunt (qv) in 1275. During his imprisonment, Art took his place and defeated Justiciar Geoffrey de Geneville (qv) in Glenmalure (1276). Despite the success of Justiciar Robert of Ufford (qv) in bringing the war to a close in 1277, the newly released Muirchertach remained disgruntled. In 1279 Bigod visited the brothers, tried to placate their grievances with gifts, and even reappointed them officials of his liberty. On 24 July 1280 Bigod's request that they be granted safe passage to England was accepted, but it is unclear whether they went. Their discontent remained and Muirchertach was again imprisoned, this time in Dublin (1281). It seems he was brought to Dunamase to negotiate with the Leinster Irish, but after the talks broke down he was returned to Dublin.
By 1282 he was free, but the Leinstermen were restless and MacMurrough was suspected of orchestrating the violence. In order to combat these disturbances (which may have connections with the Welsh success at Llandeilo Fawr in June 1282) the justiciar, Stephen de Fulbourn, decided to murder the brothers. In July 1282 they arrived under a safe conduct in the Leinster port of Arklow to take ship for England to visit Bigod; but before they could embark, they were murdered by de Fulbourn's assassins.
Muirchertach's life is representative of the fortunes of the Irish nobility of east Leinster. The first part of his career demonstrates their pragmatic attitude. But because of the sea-change in their attitude in the 1270s, Muirchertach took up arms against the English to prevent the erosion of his position. His decision signalled the emergence of widespread war in east Leinster.