O'Donnell, Sir Niall Garvach (1569–1626), Gaelic chieftain and royalist, was the son of Con, who was the head of the Clann-Dalaigh branch of the O'Donnells based in east Donegal, and his wife Rose, daughter of Shane O'Neill (qv). His grandfather Calvagh (qv) had been the O'Donnell in the 1560s but after his death in 1566 power in Tyrconnell had passed to the family of Calvagh's half-brother Aodh (qv) (d. 1600). Neither Con nor his sons ever forgot their own claims and Con, who had been brought up in the Pale, always looked to the English as a means of recovering their patrimony. Con and his sons established their own power base between the River Finn and Lough Swilly in east Donegal and were constantly at loggerheads with the ruling O'Donnells. Niall was fostered out to the MacLeans of the Western Isles of Scotland in his youth.
During the 1580s Tyrconnell was wracked by civil war and three of his brothers were killed during this time; of his eight brothers six would die violent deaths. His closest ally was his neighbour and grandfather Sir Turlough Luineach O'Neill (qv), who was trying to preserve his rule in Tyrone from the powerful challenge of Hugh O'Neill (qv), earl of Tyrone. On 1 May 1589 he fought alongside Sir Turlough when they defeated Tyrone in battle. However, this victory could not for long check the increasing might of Tyrone in Ulster. In April 1592 Aodh O'Donnell retired, to be succeeded by his son ‘Red’ Hugh (qv), who was a close ally of Tyrone. Niall conspicuously failed to attend ‘Red’ Hugh's election as O'Donnell and was in Dublin trying to secure government support. His pleas were disregarded and in July the government came to an agreement with ‘Red’ Hugh, although one of the conditions was that Niall should be treated fairly. He submitted to ‘Red’ Hugh in 1594.
O'Donnell, anxious to heal the bitter divisions within his lordship in order to focus his efforts on joining Tyrone in rebelling against the crown, decided to try to reconcile Niall to his rule instead of crushing him. Although he had not been strong enough to be a serious candidate for the title of O'Donnell, Niall did have a large following in Tyrconnell. Moreover, his undoubted martial prowess would make him a valuable ally. Their reconciliation appeared to be sealed by Niall's marriage to O'Donnell's sister Nuala (qv), and O'Donnell certainly showed great faith in his loyalty. In 1597 and 1598 he sent Niall on expeditions into Connacht, and in July 1599 left him in charge of the siege of the castle of Collooney in Sligo. However, he continued to nurture his ambitions and was discontented when O'Donnell took from him the castle of Lifford.
In late 1597 he had assured two enemies of O'Donnell imprisoned in Donegal that he would join the English if they sent a force there. In the spring of 1600 an English garrison was established at Derry under the command of Sir Henry Docwra (qv), who soon began secret negotiations with Niall. In September, O'Donnell went on a raid to Clare and left Niall in charge of the siege of the Derry garrison. At the start of October Niall went over to the English, bringing with him over 200 men. He would have brought more but O'Donnell's supporters had become aware of his dealings with the English and he had been forced to hurry to Derry before he was fully ready. He then marched with the English to Lifford, which they successfully stormed on 9 October. O'Donnell, stunned at his cousin's treachery, hurried back and besieged them. On 24 October Niall suddenly led the English out to battle. During this fracas Niall mortally wounded O'Donnell's brother Manus and only narrowly avoided being killed by his other brother, Ruaidhrí (qv). Docwra was delighted at this, as it had created a blood feud between Niall and O'Donnell, making it harder for Niall to go back, although he appears to have made some efforts to do so.
Niall's defection had transformed the military situation in north-west Ulster. He could guide the English across the difficult northern terrain and his spies provided valuable intelligence. The English could now move around Tyrconnell at will. More importantly, Niall was unmatched as an exponent of the guerrilla-style warfare that suited the local terrain. In December he went to Dublin to meet Lord Deputy Mountjoy (qv). On 18 March 1601 he was granted a custodium of Tyrconnell with the exception of Ballyshannon and the fishery of the Erne. This document also recognised him as chief of the O'Donnells. By the time he returned to Derry in April his relationship with Docwra was starting to deteriorate. He wished to rule Tyrconnell as absolutely as any of his predecessors had done, while the English wanted to extend the crown's authority to every corner of Ireland. To appease him Docwra gave him control of MacSweeney's country.
However, in April O'Donnell unexpectedly marched on him, forcing him to retreat temporarily to Derry. On 26 May 1601, on hearing Tyrone was near Lifford, he gathered a small group of Irish and English and attacked the earl's larger army. He killed 100 of Tyrone's men and chased him for miles across the country. In August he took Donegal abbey, and this virtually shut O'Donnell out of his own country unless he could immediately recapture it. Donegal abbey became the scene of a bitter and bloody month-long siege. It reached a ferocious climax on the night of 26 September when a gunpowder explosion in the abbey started a fire. Seizing his chance, O'Donnell quickly ordered an attack, resulting in a chaotic affray amid the smoke and flames. At one point defeat seemed certain for Niall, but he and his men somehow held out until the arrival of a relief force sent by Docwra forced O'Donnell to call off his attack. Niall's brother Conn Óg and 300 of his followers were killed in the battle.
The royalist victory at the battle of Kinsale in December extinguished the remnants of O'Donnell's power but, due largely to Niall, he was a broken reed by then anyway. By 1602 Niall held Tyrconnell and was de facto O'Donnell. In March he was knighted by Mountjoy. During this year the rift between him and Docwra deepened. They quarrelled over pay and the apportioning of plunder. By the year's end Niall was refusing to help or even meet him. In turn Docwra wrote to Dublin accusing him of plotting with O'Donnell and Tyrone against the crown. Given the bad blood between Niall and the rebel leaders, this charge cannot be taken seriously. Docwra may have been jealous of all the plaudits heaped upon Niall, especially by some of Docwra's own officers, many of whom had little regard for their commander's military capabilities. Moreover, Docwra, like many other servitors, was hungrily eyeing up the vast tracts of land that had fallen under crown control in Ulster.
There can be no doubt that Niall was acting in a bellicose manner towards the English, but it is far more likely that he was simply trying to extort further concessions than plotting another rebellion. In January 1603 O'Donnell's brother Ruaidhrí submitted to the English. Niall reacted with alarm to this development, correctly suspecting that the English would play Ruaidhrí against him in Tyrconnell. He responded by seizing Ruaidhrí's cattle and may even have tried to murder him. In April 1603, on hearing of O'Donnell's death in Spain, Niall had himself inaugurated as O'Donnell. By then Tyrone had submitted and Mountjoy, who genuinely seems to have intended treating Niall well but was now weary of his grandstanding, ordered his arrest. Niall escaped but was resolutely pursued by Ruaidhrí and Docwra. They captured all of his cattle, and many of his followers were either killed or starved. A hunted fugitive, Niall gave himself up and travelled to London to plead his case.
Docwra advised that he be executed or imprisoned but Niall still had his supporters at court. He was granted the lands he had held before the wars started in east Donegal. Ruaidhrí was given the rest of Donegal and was made earl of Tyrconnell. Furious at how he had been treated, Niall proudly refused formally to take out his patent for the 12,900 acres of land granted to him, although he would remain in practical possession. For the next three years he continued his vendetta with Tyrconnell and Tyrone, engaging in land disputes with both. He remained first and foremost a warrior and was unsuited to the role of a landlord: by 1608 he was in debt. In March 1607 he was wounded fighting for the government against Caffar Óg O'Donnell (qv). The flight of the earls in September 1607 seemed to open up great opportunities for him once more. However, not for the first time, he overplayed his hand – this time disastrously so.
In the early months of 1608 he appears to have encouraged Sir Cahir O'Doherty (qv), discontented at his treatment at the hands of the governor of Derry, to believe that he would join him in rebellion. However, when O'Doherty seized and burnt Derry in April, Niall stayed aloof. Niall clearly had designs on O'Doherty's territory and had been promised the ownership of it in 1607 by Lord Deputy Chichester (qv). Conversely, he refused to meet the English either. Instead he began to bargain with them over the price of his aid, demanding that he finally be recognised as lord of Tyrconnell. Through all his dealings with the English Niall had displayed a childlike cunning, even naivety. Upon the arrival of royal forces in the region in late May, he hastened to their side and offered to assist them in catching O'Doherty. However, he seems to have kept in touch with the rebel leader, warning him of the royal forces' movements. The English soon became suspicious and arrested him on 15 June. He was immediately sent by ship to Dublin where he was imprisoned in Dublin castle and charged on six counts of treason. Many of O'Doherty's adherents including his wife subsequently implicated O'Donnell in the failed insurrection. Clearly he had compromised himself but the charge that he was in league with Tyrone and the Spanish was pure fantasy. In June 1609 he was tried before the court of king's bench for treason. However, the Donegal jury, suitably fortified both by fears of retribution from Niall's kinsfolk and by threats of excommunication from the catholic clergy, refused to convict, despite coming under considerable pressure from the government to do so. After three days, realising that the jury was about to acquit him, the attorney general dismissed them. During his period in confinement Niall had made numerous attempts to escape. In order to safeguard against this he was sent to the Tower of London in October 1609. Despite the brazen illegality of these proceedings, there he died in 1626.
Niall's wife, Nuala, disowned him after his defection to the English in 1600. She joined Tyrconnell and Tyrone on their flight into exile in 1607. He had two sons: Naughton, who died in the Tower of London in 1640, and Manus, who served as a colonel in the army of the catholic confederation under Owen Roe O'Neill (qv) and died at the battle of Benburb in 1646.