MacMurrough, Muircheartach (c.1495–1547), Gaelic warlord, was probably eldest of the six sons of Art Buidhe Kavanagh (d. 1517), king of Leinster. After the death of Art Buidhe at the friary of Enniscorthy (25 November 1517), Muircheartach apparently became leader of his family's faction of the MacMurrough Kavanaghs, the Sliocht Domhnall Riabhach. However, Art's death ensured that there was a disputed succession between his brother, Gerald Kavanagh (d. 1523), and Muircheartach, son of Murchadh Ballach MacMurrough (qv) (d. 1512). It seems that Muircheartach son of Art threw his weight behind his brother's bid for the Leinster kingship, helping to ensure Gerald's electoral victory over the son of Murchadh Ballach. Moreover, Muircheartach (it appears) was to remain close to the Fitzgeralds of Kildare – though his role during the 1534–5 rebellion of Thomas Fitzgerald (qv) (d. 1537), 10th earl of Kildare, is uncertain. He was to witness the indenture made between Cathaoir mac na hInghine Crosda (‘MacInnycross’) MacMurrough (qv), king of Leinster (d. 1544), and the lord deputy, Leonard Grey (qv), on 14 July 1536.
The implosion of the Kildare dominance over Leinster brought Muircheartach considerable opportunities. Like his kinsman the youthful Domhnall mac Cathaoir MacMurrough Kavanagh (qv) (d. c.1542) of Garryhill, and Sean O'Byrne (qv), lord of the mountainous lordship of Crioch Raghnuill in Wicklow, Muircheartach had formed alliances with the mercurial Toirdhealbhach O'Toole (qv), overlord of the O'Tooles. This alliance between Muircheartach and Toirdhealbhach was sealed, at an uncertain date, through the marriage of O'Toole to Sadhbh MacMurrough, daughter of Muircheartach, in the great hall of Clonmullen castle, Co. Carlow. In the 1540s, though, the government was to refer to this marriage derisively as a mere hand-fastening.
In May 1540 links between Muircheartach and Toirdhealbhach were further exposed in the letter of the Dublin council to Thomas Cromwell, chief minister of Henry VIII. Among a series of complaints against Leonard Grey, the council accused him of releasing, without any constraints, a troublesome son of Muircheartach. Once free, the son of Muircheartach, bent on inflicting damage on the Pale, gathered a force and rode to Toirdhealbhach. No doubt Muircheartach's forces were instrumental during June 1540 in aiding Toirdhealbhach and Domhnall mac Cathaoir Kavanagh to defend the O'Tooles’ country successfully from the government. But neither he, Domhnall mac Cathaoir Kavanagh, nor Cathaoir MacInnycross were able to resist the July invasion of Idrone by James Butler (qv) (d. 1546), 9th earl of Ormond. Even though Domhnall mac Cathaoir Kavanagh, briefly aided by Toirdhealbhach, continued to harass the Butlers, Muircheartach and his fellow nobles chose to submit.
Ormond's campaign into Idrone heralded the Dublin administration's programme to reduce the MacMurroughs. In August and September 1540 the MacMurroughs and the O'Byrnes were forced to come to peace by the lord deputy, Sir Anthony St Leger (qv), forcing Cathaoir MacInnycross to renounce his title. St Leger and Ormond completed their circuit in east Leinster in November by bringing about the submission of Muircheartach O'Toole's son-in-law. Unlike Domhnall mac Cathaoir Kavanagh or Cathaoir mac Airt MacMurrough (qv), Muircheartach did not find favour in the eyes of Ormond. In November 1540 neither Muircheartach nor Cathaoir MacInnycross were included as pensioners in Ormond's plans for the reformation of Leinster. This may have been because of their former attachment to the now defunct Kildare party in Leinster. It is clear though that Muircheartach remained close to the ailing Cathaoir MacInnycross, and witnessed his humiliating indenture with St Leger (3 September 1543). This treaty actually facilitated the rise of Cathaoir mac Airt to become the most powerful of the MacMurroughs, as Cathaoir MacInnycross relinquished much of his personal power.
Muircheartach was to be rewarded for his loyalty, as he succeeded Cathaoir MacInnycross some time in 1544. What Cathaoir mac Airt thought of this is unrecorded, but it seems probable that he reached some kind of deal with the now ageing Muircheartach concerning the future succession. Equally, Muircheartach managed to stand aloof from the murderous feud emerging between the Kavanaghs of Garryhill and Cathaoir mac Airt. Headed by Gerald mac Cathaoir Kavanagh (qv) (d. c.1549), the Kavanaghs of Garryhill were determined to challenge their old tormentor, Cathaoir mac Airt. In 1545, when Gerald mac Cathaoir tried to position himself as a potential successor, Muircheartach side-stepped the issue, leaving the bitter rivals to fight it out in a pitched battle at Hacketstown, Co. Carlow. Even though Gerald mac Cathaoir had the support of his Gabhal Raghnaill O'Byrne cousins (also Muircheartach's old allies), Cathaoir mac Airt emerged from the slaughter at Hacketstown victorious. What Muircheartach thought of this major shift in the political equilibrium towards Cathaoir mac Airt is not known. Instead he chose to live out his few remaining years in relative peace, and died in 1547, leaving the MacMurrough title to Cathaoir mac Airt. The genealogies accord him five sons and a daughter.