O'Byrne, Brian (1593–1653), lord of Crioch Raghnuill, was the eldest son of Feilim O'Byrne (qv) (d. 1631), lord of Crioch Raghnuill, and Una O'Toole (d. 1628), daughter of Fiach O'Toole (qv) (d. 1578), lord of Fartry and Ferter. Brian's early childhood was spent in the turmoil caused by the government campaigns against his famous grandfather, Fiach MacHugh O'Byrne (qv). After Fiach was killed in Glenmalure on 8 May 1597 Phelim was forced in January 1598 to respect a truce with the government. But the ‘wolf of the mountain’ returned to war in late 1598 and for two years was involved in attack and counterattack against government forces. In December 1600 the English under Charles Blount (qv), Lord Mountjoy and lord deputy of Ireland, surprised Phelim at his house of Ballinacor, capturing several prisoners, Una and Brian among them, though Phelim himself managed to escape. The boy and his mother were released only in March 1601 after the final submission of Phelim and his brother Reamain O'Byrne (d. c.1642). Thereafter, Phelim strove to keep his family loyal, serving as a justice of the peace and as a member of parliament for Wicklow.
As Phelim's heir, Brian seems to have been reasonably well educated and was groomed to assume his father's position, but Phelim's favour towards one of his younger sons, the talented Aodh O'Byrne (qv) (d. c.1660), gave rise to implacable rivalry between them. In January 1630 Phelim commented on their feud by introducing a clause into his will to protect his gift to Aodh, writing that he did ‘desire my son and heir Bryan McPhelim not to meddle with the same unless only for the right of my said son Hugh’). Brian married Mary O'Dempsey, daughter of Sir Terence O'Dempsey, later 1st Viscount Clanmaliere; they had one recorded child, Seán mac Brian O'Byrne (d. c.1652), but their marriage was short-lived, ending in an unsuccessful attempt by Brian and his father to have her executed on capital charges, the details of which are unknown. With another woman Brian fathered a natural son, Muircheartach O'Byrne (d. c.1631).
On 24 February 1616 Sir Richard Graham obtained title to the lands of Phelim and Brian lying in Cosha, a region between Aughrim and Shillelagh. Phelim contested this decision, but an inquiry at Wicklow ruled on 18 December 1617 that he had forfeited all rights of inheritance to the Cosha lands. Brian and his father continued to contest this through the law courts, but the lands effectively belonged to Graham, now high sheriff of Wicklow. Their fortunes worsened after the appointment on 8 September 1622 of Henry Cary (qv), Viscount Falkland, as lord deputy of Ireland, who wanted to establish a plantation in Wicklow on O'Byrne lands and arranged to have the crown's title found by inquisition in August 1623. Conflicting court interests proved to be in Phelim's favour and the duke of Lennox and the earl of Middlesex combined to have the project halted in October. Early in the following year Brian was sent to London to present a petition to James I, complaining about the acquisition by Graham of the lands in Cosha. He won support at the council table for his plea to prevent Sir James fitz Piers Fitzgerald of Ballyshannon from acquiring letters patent to his family's lands, and gained the king's letters instructing Falkland to desist from granting away any more of Phelim's territory. However, after Brian's return from England, Sir William Parsons (qv) disregarded the royal letters, obtaining a warrant from Falkland to occupy some of the O'Byrne holdings.
Falkland and his allies now moved against the O'Byrnes. On the basis of fabricated evidence, on 13 March 1626 Falkland committed Brian and his brother Toirdhealbhach O'Byrne to close confinement in Dublin castle, claiming that he had ‘pregnant proofs of their involvement in a conspiracy to revolt’. To prevent a future rebellion, the lord deputy recommended the wholesale plantation of Crioch Raghnuill, but this request was denied by the commissioners for Irish affairs. The brothers remained in captivity until 20 August, when intervention from England compelled Falkland to release Toirdhealbhach and permit Brian freedom of movement within the castle; a petition to the council resulted in Brian's release on 24 December, pending trial. He tried to leave for England to petition Charles I, but was prevented by the terms on which he had been freed. On information lodged by one Art Kavanagh, Brian and Toirdhealbhach were again committed to Dublin castle on 2 November 1627 and were miserably treated, denied food and placed in irons.
The accusations against the O'Byrnes centred on the actions of Phelim as justice of the peace. In 1625 he had apprehended, tried, and hanged a Brian Kavanagh and others for the murder of a land speculator, the Rev. Robert Ponte of Rathdrum, who was also a justice of the peace. It was suspected, though, that Phelim himself had authorised Ponte's murder and that Brian's brother Aodh was the murderer. Phelim's brother Reamain, now his enemy, joined forces with Cathaoir O'Byrne and Laurence, Lord Esmond (qv), to accuse him and his sons of the murder. Falkland and his administration gathered evidence against Phelim in a series of depositions. A commission was also established to investigate Phelim's title to Crioch Raghnuill. In August 1628 Phelim and his sons were indicted of Ponte's murder and committed to Dublin castle to await their trial before the king's bench. Phelim's wife, Una, on receiving the news, suffered a heart attack and died within a few days. Phelim, however, had gained an influential patron at court in the earl of Carlisle, who had recently acquired interests in Wicklow and whose Irish agent's father was married to Phelim's daughter. With Carlisle's assistance, the case was decided in favour of the O'Byrnes. In December the commissioners for Irish affairs with the support of the English privy council ordered that Phelim and his sons be released, but increased the rents payable to the crown for tenure of their lands. Subsequent inquiries into the episode contributed to the recall of Falkland in August 1629.
Brian succeeded his father as lord of Crioch Raghnuill upon the latter's death between 1 January and 24 January 1631. He was embittered by his experiences of the 1620s and deeply resented the planters; during summer 1631 he made no attempt to restrain the raids of his son Muircheartach upon the lands of Esmond. Besides becoming lord of Crioch Raghnuill, Brian also succeeded his father as a patron of poets, commissioning some fine poems in his own honour, and as member of parliament for Wicklow county; he was returned at the election of 1634 but in 1640 lost his seat to New English planters, as did his cousin James O'Byrne. These electoral losses, combined with further planter inroads, created great tension in the lordship. Brian and his cousin Fiach O'Toole (qv) of Castlekevin (d. 1653) secretly planned the complete overthrow of the plantation of Wicklow, and in late October 1641 attacked and expelled the settlers from the mountains. According to the depositions given by the ousted settlers, Brian and his son Seán were the main perpetrators of the attack.
In the following period Brian was eclipsed by his younger brother Aodh, who had spent much of the previous decade in the Spanish army, campaigning in Europe. He was a good soldier, an astute politician, and an attractive personality, and was consequently more popular than Brian with the Old English catholics who dominated the Catholic Confederation in Kilkenny. In 1646 and 1647 Brian reappeared, leading the opposition of Wicklow's catholic gentry to the confederation's demands for the supply of its troops. Their obduracy arose from their being excluded from the confederation's army of Leinster, one reason for which was Brian's support of Owen Roe O'Neill (qv), commander of the army of Ulster. On 8 August 1647 Aodh was captured by parliamentarian forces during the defeat of the Leinster army at the battle of Dungan's Hill. Taking advantage of his absence, Brian moved even closer to the party of O'Neill and the papal nuncio GianBattista Rinuccini (qv), allowing O'Neill and his army to camp in Wicklow; he also supported them after the confederacy split in May 1648, protecting their messengers from the allies of James Butler (qv), marquess of Ormond.
Brian's fortunes changed after O'Neill obtained the release of Aodh from the parliamentarians in September 1648. Aodh turned on O'Neill and accepted the appointment of governor of Wicklow on 20 September, using his position to subdue his brother and strengthen the defences of Carnew and Arklow. Brian now determined to vanquish Aodh for once and for all, and with the help of some highland troops of Randall MacDonnell (qv), marquis of Antrim, attacked him in March 1649. But the arrival of Oliver Cromwell (qv) in Ireland on 15 August led to a rapprochement among the various factions of anti-parliamentarian forces. On 9 September Charles II wrote to Brian, urging him to fight for him, and promising him royal favour in return; and as the O'Neill and Ormond parties moved together to fight Cromwell, O'Neill ordered Brian to join the struggle against the parliamentarians. On 20 October 1649 Brian's position was recognised in a treaty between O'Neill and Ormond, granting his forces legitimacy. The brothers then set aside their differences and worked together to oppose the progress of Cromwell's army into the mountains of Wicklow. In November and December they besieged Arklow but withdrew before a large parliamentarian force, and in January 1650, when they reappeared before Arklow, the garrison defeated them. Despite these set-backs they recovered, and held large parts of Wicklow and Wexford throughout 1651.
That year Brian travelled with 200 Leinster catholics to serve in Connacht, and with Rory O'More (qv) attended the ecclesiastical congregation of the clergy of the province of Dublin on 24 September, taking oaths for the renewal of the confederation. Brian and Aodh enjoyed further successes against the English into 1652, but the final surrender of the Leinster army on 12 May proved their undoing; they were excluded from the terms of the surrender and a reward of £400 was placed on their heads. Sensing that their support was wavering, General Edmund Ludlow (qv), with 4,000 soldiers, laid waste the crops in Wicklow and Wexford in July and then offered protection to those who would submit. The result was wholesale desertion from the forces of Brian and Aodh, exposing them to the constant danger of betrayal. They were forced to flee from Wicklow. Aodh disguised himself and took ship for Europe, while Brian resolved ‘to liue and dye there with the poor Ulstermen’. After many dangers he reached Ulster, and then went on to Connacht to the island of Inishbofin off the Galway coast. It is probable, though not certain, that the last lord of Crioch Raghnuill was killed on 15 December 1652 when parliamentarian forces occupied the island. His son and heir, Seán, managed to escape to France, and died there.