O'Byrne (Ó Broin), Murchad (d. 1338), lord of the O'Byrnes and probably eldest son of Gearóid O'Byrne (Ó Broin ) (d. c.1293 ), lord of the O'Byrnes, was at times the most powerful Irish aristocrat in Leinster during the first three decades of the fourteenth century. Gearóid succeeded to the O'Byrne lordship in about 1268, but was immediately threatened by the thirst of the Butlers for territory in the central Wicklow highlands. This created a tense atmosphere in the mountains in the late 1260s. But the sparks that really ignited the Wicklow Irish were famine, worsening weather, and poor English decisions resulting from the initial insensitivity of Archbishop Fulk de Sandford (qv) of Dublin. The violence must have been considerable and widespread, given the reaction of the English. No less a figure than Henry III's nephew was dispatched to Glenmalure either in late 1269 or early 1270. Once there, Henry of Almain (d. 1271), son of Richard (d. 1272), duke of Cornwall, quelled disturbances. But his campaign failed to stamp out decisively the glowing embers of Irish anger towards the archbishop's officers. By July 1270 the war in the Leinster mountains had clearly reached crisis proportions, leading to a directive to the justiciar, James de Audley (qv), to aid the archbishop against what was termed a ‘malicious rebellion’ (quoted in J. T. Gilbert (ed.), Historic and municipal documents of Ireland, 1170–1320 (1870), 183). The slow emergence of war coincided with the marked decline of existing Irish dynastic elites, and the appearance of new hard-line leaders like Gearóid. These factors fuelled the rapid spread of the war throughout the Leinster mountains, illustrating a massive political shift among the Irish of east Leinster. Belatedly Fulk realised his blunder and sent his envoy in 1270–71 among the Irish. To a large extent his diplomatic tacking succeeded, and peace was restored. But Fulk's death in May 1271 and that of his absentee successor, John of Darlington, in 1284, resulted in a prolonged archiepiscopal vacancy. This led to the disastrous intrusion of royal officials with their hard-edged attitudes into the lands of the Irish, destroying any possible return to the previous modus vivendi. Then a disaster of biblical proportions struck the Irish in the form of a combination of heavy snow, plague, and rainstorms. With their economic base destroyed, Gearóid and his followers burned English settlements from the mountains to the sea. Any influence the archbishopric had had, evaporated. And at Glendalough Gearóid and the O'Tooles (Uí Thuathail) defied an army led by de Audley before June 1272, and another under Maurice fitz Maurice FitzGerald (qv) between June 1272 and April 1273.
Between 1269 and 1273 Muirchertach MacMurrough (qv), the traditional overlord of the O'Byrnes and O'Tooles, was hesitant to enter the war. But his fear of Gearóid outweighed his fear of English censure, leading him to safeguard his traditional position by assuming leadership of the war against the English. Indeed, the combined strength of Gearóid and Muirchertach along with the O'Tooles proved devastating, as evidenced by the scale of the English defeat at Glenmalure in 1274. Despite Muirchertach's capture in 1275, Gearóid and the rest of the Irish of east Leinster continued to prosper under the leadership of Art MacMurrough, brother of Muirchertach. Together they routed the justiciar Geoffrey de Geneville (qv) at Glenmalure in 1276; but de Geneville's successor, Robert of Ufford (qv), successfully subdued them in 1277–8. In 1282 Gearóid's rising stock in east Leinster was boosted by the government's assassination of Muirchertach and Art at Arklow in July 1282. But having said that, the brothers' leadership of the Leinster war between 1274 and 1278 had secured MacMurrough suzerainty over the Irish of east Leinster, despite Gearóid's attempts to outshine them in the late 1280s. Gearóid seems to have died c.1293; Murchad, his son, succeeded.
At first Murchad grudgingly acknowledged MacMurrough primacy over the Irish of east Leinster. This was clearly illustrated on 19 July 1295 when Muiris (qv) son of Muirchertach MacMurrough submitted to the English on his behalf and that of the O'Tooles. However, the political balance among the Irish of east Leinster during the early fourteenth century shifted in favour of Murchad. This shift was linked with the politics of wider Leinster. The dynamics of west Leinster had changed dramatically in the early years of the century as a result of the decline of the military power of the O'Melaghlins (Uí Máelshechlainn) of Westmeath from 1290 onwards, and the murders of several leaders of the O'Connors of Offaly (Uí Chonchobair Failge) in June 1305. These acts switched the orientation of the theatre of war from west Leinster southwards to Laois and Munster, as evidenced by the rise of Laoiseac O'More (qv) of Laois. In turn this shifted the existing delicate political balance among the Irish of east Leinster in favour of Murchad. Essentially, what drove the O'Byrnes forward was the geographical location of their lordship. The fundamental problems of the O'Byrne territories were that much of the cultivable soil of the lordship was poor: so poor that at times its inhabitants were vulnerable to harvest failures, animal plagues, and ultimately famine. Furthermore, potential enemies, both English and Irish, surrounded the O'Byrnes. If his lordship was to survive, Murchad had to expand to gain the necessary living space required to secure his power. One of the secrets of his later success was the tight rein maintained by his family, the Gabal Dúnlaing, on rival kinsmen. In contrast to the O'Tooles and MacMurroughs of this period, the O'Byrnes proved a more homogeneous force. This relative unity of purpose allowed Murchad to harness the military potency of his lordship to exploit the gradual meeting of the ambitions of the Irish of both parts of Leinster along the Barrow valley. Thus, Murchad was able to extend an alliance to Laísech O'More, and by exploiting divisions among the English and creating new alliances with the O'Tooles of Imaal and the Ostmen of north Wicklow, O'Byrne's rise was assured. Despite the movement of the wider politics in his favour, this may not have been immediately obvious to Murchad, as he did not break with Muiris MacMurrough till 1308 at the earliest. Indeed, the concord of 1295 held for about six years, but the war that Muiris and Murchad waged on the English, during winter 1301–2, signalled the recommencement of hostilities. Primarily Murchad's expansion was directed against the English of east Wicklow, particularly those of the strategically important Glenealy valley. The year 1305 proved a turning point in the history of the Irish of Leinster. The murders of the O'Connors of Offaly and of four MacMurrough leaders dramatically accelerated the growing cooperation between the Irish of east and west Leinster. This point is borne out by the burning of Ballymore in the western foothills of the Wicklow mountains by the O'Mores in May 1306. Significantly, the justiciar, Sir John Wogan (qv) retaliated by attacking Murchad. But in a battle in Glenealy Murchad and the Leinstermen, along with other Irish forces, destroyed Wogan's army. By early 1307 the Dublin government was in crisis in Leinster. However, by summer 1307 the crisis had been subdued, Murchad Ballach MacMurrough, one of the principal leaders, having been killed on 1 April. But the most decisive English move in defusing the crisis was their tempting of Murchad. In return for his good behaviour, in 1307 Murchad was given the confiscated Glenealy lands of Risdeárd O'Toole. The English government hoped that his taking of this bait would ignite a war between the O'Byrnes and the O'Tooles. Predictably this happened, but the O'Byrnes were too strong for the O'Tooles and the English. In 1308 the O'Tooles, still smarting from their losses, turned on the English. In response Wogan brought an army into Wicklow in June 1308 against the O'Tooles. Clearly he expected the O'Byrnes to allow him to corner the O'Tooles. Instead, at Glenmalure he found waiting for him the O'Tooles and Murchad, who routed his force.
During this period, a struggle gradually emerged between Murchad and Muiris MacMurrough. This struggle dominated the Irish of east Leinster, delaying their attempts to promote alliances with the Irish of west Leinster. The first fluttering of this conflict came during the de Cauntetoun rebellion against Edward II during 1308–10. During this struggle both the O'Byrnes and the MacMurroughs rushed to support the protagonists. Aside from his feud with the MacMurroughs, Murchad directed much of his energy against the settlers, eradicating the weakening grip of the FitzGeralds on the barony of Wicklow. In 1308, during a suit before the Dublin bench, Murchad, in absentia, was among those charged with the seizure of rents at Wicklow which had been extracted by George de la Roche, one of the co-heirs of the barony. However, Murchad's advance was temporarily halted by the army of Piers Gaveston (qv) with the help of Énrí O'Toole in 1309. After 1309 Murchad began to consolidate his grip over south Wicklow, wresting Glenmalure from the O'Tooles by 1310 as well as raiding Kildare and the MacMurroughs in Carlow and north Wexford. When faced by the O'Byrne threat along his northern frontier, Muiris, like Énrí O'Toole, moved decisively to block them by allying with the government. And the MacMurrough determination to curtail Murchad's ambition is evidenced by Muiris's service alongside Wogan in the Leinster mountains between June and August 1311. MacMurrough fears were well founded, having their roots in the wars of the 1270s. Indeed, the wooing of the O'Nolans (Uí Nualláin) by Murchad and the rewards for service against him probably decided the matter for them. However, Murchad suffered a considerable setback during Lent 1313, when he was completely overthrown in Glenmalure by Lord Edmund Butler (qv). Shortly afterwards, it seems, Muiris died and was succeeded by the obscure Domnall Riabach MacMurrough, of whom virtually nothing can be discerned. What appears clear is that the O'Byrnes quickly recovered and temporarily superseded the MacMurroughs as the most powerful Irish dynasty of east Leinster. It was the chaos caused by the devastating campaigns in Leinster of Edward Bruce (qv) during 1315–18 that greatly aided Murchad's destruction of English power in east Wicklow. With his allies, Murchad burnt English settlements from Bray to Arklow, destroying the FitzGerald baronial caput of Wicklow twice in 1315–16. However, his ambition was dented by Edmund Butler's defeats of the O'Mores in late 1315 and early 1316. The next year proved to be Murchad's high-water mark, as after mid 1316 his support was eroded by the defeats of his allies. As Bruce's threat began to recede in 1316–17, the English took the offensive. In September 1317 the lord lieutenant, Roger Mortimer (qv), routed the O'Tooles of Imaal before defeating Murchad and the Archbolds in Glenealy, east Wicklow, forcing Murchad to submit at Dublin. This did not, however, bring peace to the region: now that their leadership of the Irish of east Leinster was more secure, the MacMurroughs simply resumed their attacks on the English of the Barrow valley.
Between 1317 and 1320 Murchad maintained a low profile, and there is considerable uncertainty as to the identity of the successor of Domnall Riabach MacMurrough. In 1320 Thomas of Brotherton (d. 1338), earl of Norfolk, appointed Henry Traherne (fl. 1330) seneschal of his liberty of Carlow. During 1323 Traherne killed the unnamed MacMurrough overlord and Énrí O'Nolan. The new MacMurrough overlord was Domhnall mac Art MacMurrough (qv). He was determined to mend fences with Murchad and succeeded in his endeavour, resulting in joint campaigns against the settlers of the Barrow. Unsurprisingly this led to two English expeditions into Uí Cheinnselaig (south Wicklow and north Wexford) in 1324. Indeed, this rapprochement may have culminated in Domnall mac Art's election as king of Leinster at an assembly in 1328. From the reaction of the English, this was a major development among the Irish of east Leinster. That Domnall mac Art embarked upon a circuit through O'Byrne and O'Toole lands, before planting his banner less than two leagues from Dublin, adds further significance. For all his efforts, Domnall was quickly apprehended by Traherne, and imprisoned till his dramatic escape from Dublin in January 1331.
During Domnall's imprisonment, Murchad rebuilt his position throughout 1329, steadily pushing the English out of east Wicklow. And instead of attacking the MacMurroughs, he opted for the subtler option of a marriage alliance, arranging the marriage of a daughter of his son Philip O'Byrne (fl. 1334) to Art, the son of Domnall mac Art's rival for the MacMurrough leadership, Muirchertach mac Muiris MacMurrough (d. 1354). This represents a considerable change of policy. Effectively the O'Byrnes were realigning with the family of their bitter rival Muiris MacMurrough. However, the escape of Domnall mac Art from Dublin (January 1331) disrupted Murchad's plans, but he recognised Domnall's suzerainty and aided in unleashing the Leinster wars of 1331–2. By winter 1331 Murchad and his new MacMurrough in-laws had tired of Domnall mac Art. Realising that his long confinement had cost him much of his overlordship, Domnall took sides with the government against them. On 1 March 1335 the O'Byrnes agreed to the terms of a negotiated peace with the justiciar, John Darcy (qv), whereby the now aged Murchad and his wife agreed to live in an English settlement under their protection. The apparent retirement of Murchad and the slow emergence of his son Tadc gave Domnall mac Art some breathing space, allowing him to campaign for Edward III in Scotland in 1335. Soon after Domhnall's return, a MacMurrough civil war erupted between him and Muirchertach mac Muiris, Murchad's ally. During the opening phase of their dispute Domnall mac Airt clearly held the upper hand, defeating his rival. This defeat forced Muirchertach to seek help from Murchad, inviting the O'Byrne branch known as the Gabal tSiomóin to settle in his Idrone lands in return for their military support. Indeed, this infusion of military muscle proved decisive, enabling Muirchertach mac Muiris to force more favourable division of Uí Cheinnselaig territory between 1335 and 1347. This renewed O'Byrne meddling within the MacMurrough ambit is reflected in their victory with Domnall mac Art over the English of Wexford in 1336, as well as Ormond's (qv) Arklow campaign of 1337. Even more startling for the MacMurrough king of Leinster was the reactivation of Murchad's plans to supersede them as principal Irish king in Leinster. At some point between June 1335 and October 1337, Prior Roger Outlaw (qv) of Kilmainham, deputy justiciar of Ireland, treated with Murchad in the O'Nolan heartland of Fotherd, indicating that the latter was acting on behalf of some of the Leinster Irish. However, Murchad's schemes never came to fruition, as he seems to have died suddenly during 1338 , leaving a disputed O'Byrne succession.