MacMahon, Heber (Ever, Emer) (1600–50), catholic bishop of Clogher, confederate politician, and military commander, was born in the barony of Farney in Co. Monaghan. His parents were probably Turlough MacMahon and Eva O'Neill. It seems that Heber's family fell on hard times and that he spent his youth living in poverty. However, the assertion that his family moved to Killybegs in Co. Donegal, where Heber was educated by the Franciscans, is an error. In fact he was educated in his native territory by the Franciscans of Kiltybegs in Farney, Co. Monaghan.
In 1617 MacMahon entered the Irish college at Douai. By 1625 he was studying at Louvain, where he became the first recipient of a scholarship for students from the diocese of Clogher. While at Louvain he was taught by Aodh Mac Cathmhaoil (qv) (Hugh MacCaghwell), and it was here that he first met the Irish émigré officer, Owen Roe O'Neill (qv), who was in Spanish service. MacMahon received a doctorate of divinity from Louvain and was appointed superior of the pastoral college there. In 1628 he became involved in a plot to secure the assistance of Cardinal Richelieu for a projected invasion of Ireland. Nothing came of it and in 1633 MacMahon returned to Ireland where he became vicar-apostolic of Clogher. He retained his links with the Irish exiles, in 1635 apparently recruiting some 3,000 Palesmen for Owen Roe O'Neill's regiment in Flanders.
In the lead up to the 1641 rebellion, MacMahon acted as Owen Roe O'Neill's agent in Ireland (Contemporary history, i, 398). Although present at a meeting which plotted the seizure of Dublin castle, he was not central to preparations for the rising. A number of depositions place him at Carrickmacross in Co. Monaghan when the rising broke out in October 1641. In March 1642 he was present at the provincial synod held at Kells, and in May he attended the national synod of the Irish clergy at Kilkenny. In the same year he was appointed bishop of Down and Connor. When O'Neill landed with his Spanish veterans in Co. Donegal in July 1642, MacMahon travelled to Doe castle to meet him. He remained a staunch adherent of O'Neill and the two men became leading figures in catholic Ulster. MacMahon himself was appointed one of the six Ulster representatives on the confederate supreme council.
In 1643 he was translated to his native diocese of Clogher, being consecrated in Kilkenny cathedral. At first he was not a very experienced politician but by 1644 he had become important in the Ulster confederate leadership. MacMahon supported the papal agent PierFrancesco Scarampi (qv), and in turn the papal nuncio, GianBattista Rinuccini (qv), who came to Ireland in autumn 1645. MacMahon played an important role in reconciling Owen Roe and Sir Phelim O'Neill (qv) just before the victory of the Ulster army at Benburb in June 1646, and following this confederate victory he was a leading opponent of the first Ormond Peace, participating in the excommunication of its proponents. From August to November 1646 he was in communication with Thomas Preston (qv), the Leinster confederate general, encouraging him to join Owen Roe O'Neill's attack on Dublin. Following the failure of the Dublin campaign, MacMahon remained a supporter of the papal nuncio. In 1647 his opponents in the confederate government attempted to have him sent to France with Viscount Muskerry (qv) on a mission to meet Charles I's consort, Queen Henrietta Maria. MacMahon caused a crisis in the confederate general assembly when he refused to go and was confined to Kilkenny city. He was replaced on the embassy by the marquis of Antrim (qv). However, as the unity of the confederates disintegrated and the opponents of the nuncio's party gained the upper hand, MacMahon's personal safety in Kilkenny was threatened; he managed to escape the city. He then played an important role in calming Owen Row O'Neill when a mutiny broke out in the Ulster army. In 1648 he continued to support Rinuccini in opposing the Inchiquin truce and was proclaimed, along with Owen Roe, in September 1648 by the confederate general assembly as ‘being traitorously disaffected to his Majesty's interest, and the quiet of this land’ (Contemporary history, 749).
In March 1649 MacMahon was captured at Castleblaney, Co. Monaghan, by the forces of Sir Phelim O'Neill and imprisoned in Charlemont fort (Contemporary history, i, 777). He was not confined for long, managing to bribe his guards and escape through a window in the main house in the fort. By now he was being called ‘the most dangerous person in the kingdom’, and Owen Roe's ‘chief confidant’. As 1649 progressed and Owen Roe became reconciled to the royalists in Ireland, MacMahon came to be trusted by the lord lieutenant, the marquess of Ormond (qv). With Turlough O'Boyle, a Donegal nobleman, he negotiated with royalist emissaries and was treated as ‘a commissioner in the behalf of General Owen O'Neill and his adherents’. On 20 October 1649 he and O'Boyle signed ‘Articles of agreement’ with the royalists. As Owen Roe fell ill, MacMahon and Lt-Gen. Richard Farrell were entrusted with leading the Ulster army south to join the royalist forces opposing the parliamentarians. In December 1649 MacMahon was prominent at a meeting of the catholic bishops which was held at Clonmacnoise.
When Owen Roe O'Neill died on 6 November 1649, a provincial council was called for 18 March 1650 at Belturbet Co. Cavan. Here MacMahon was selected as a compromise candidate to succeed Owen Roe as commander of the Ulster army, defeating other more qualified candidates such as Owen Roe's son Henry, his nephew, Hugh Dubh O'Neill (qv), and Richard Farrell. (In fact MacMahon's two main rival candidates at the provincial council were Daniel O'Neill (qv) and the marquis of Antrim.) The anonymous author of the Aphorismical discovery considered that MacMahon was not ‘by descent, function, practice in the art, or any other quality’ fitted for such a role (Aphorismical discovery, ii, 70).
MacMahon took his duties seriously, although he once stated ‘As for the election of me, by the Irish gentry of the province, I gain nothing by it but troubles’ (MacMahon to Sir George Monro, 20 Apr. 1650, Contemporary history, ii, 391). He travelled south to meet Ormond and then took his army to Ulster to begin recruiting. He received a commission as commander of the ‘native Irish of Ulster’ for king Charles II, with authorisation to lead the Ulster army and in June 1650 took the field against parliamentarian forces in Ulster with an army of 4,000 infantry and 600 cavalry. His men took Dungiven castle in Derry and Ballycastle in Antrim and won a number of skirmishes with the forces of Sir Charles Coote (qv). He then retreated with the Ulster army to the River Foyle and won another engagement with Coote's forces while fording the river at Lifford. He then took up a very strong position with his army on a mountain-side near Letterkenny in north county Donegal.
Although short of ammunition and lacking a detachment he had allowed to march off to attack Doe castle, MacMahon decided to give battle on 21 June 1650 to a reinforced Coote at the ford of Scarrifhollis on the river Swilly near Letterkenny. Owen Roe O'Neill's son Henry had advised MacMahon not to fight but, as the Aphorismical discovery describes it, MacMahon and his army put themselves ‘in a distracted posture of battle, where their horse could scarce relieve the foot’ (Contemporary history, 84–6). MacMahon's force of 3,000 infantry was divided into two brigades commanded by Henry O'Neill and Phelim McToole O'Neill. Although initially the Ulster army fought well, an attack by the parliamentarian cavalry caused disaster and the Irish fled. Some 2,000 of MacMahon's men were killed in the battle and 1,000 more in the ensuing rout. In all MacMahon lost nine colonels and generals (including Henry O'Neill, who was executed after being taken prisoner), four lieutenant-colonels, three majors, and twenty captains, a disaster from which the catholic nobility of Ulster never recovered.
MacMahon himself escaped the destruction of his army and fled southwards with Richard O'Farrell and 200 cavalry. However, two days later he was betrayed in Co. Fermanagh by one of the Maguires and captured at Glendorrochy after a fight, in which he was wounded, by Major John King (qv) (d. 1676). MacMahon was kept imprisoned in Enniskillen castle for an unclear period ‘till his thigh bone was knit’, and then executed on the orders of Charles Coote, although Major King attempted to protect him. His death was reported in Mercurius Politicus under the date 5 July 1650, although this may be too early. His head was spiked on Enniskillen castle although his body was released for burial on Devenish Island on Lough Erne.
Bishop Heber MacMahon's role as one of the more important Ulster confederate leaders was substantial. Rinuccini regarded him as being motivated purely by political matters. The historian Tadhg Ó hAnnracháin points out that he was more a supporter of General Owen Roe O'Neill than the extreme clerical faction amongst the catholic confederates (Ó hAnnracháin, Catholic reformation, 173). As commander of the Ulster army he was a failure. Elected solely as a compromise candidate, he was unqualified for the role. His actions at Scarrifhollis, dividing his forces and then ignoring the advice of Henry O'Neill, led his army to disaster.