Bagenal (O'Neill), Mabel (c.1571–95), countess of Tyrone , was born in Newry, sixth daughter and youngest among eleven children of Sir Nicholas Bagenal (qv), marshal of the army in Ireland, and Eleanor Griffith of Penrhyn, Wales. At his death in 1590, Sir Nicholas charged his son and successor in office, Henry (qv), with the ‘careful disposing’ of Mabel, who had earlier attracted the interest of Turlough Luineach O'Neill (qv) (d. 1595).
Shortly after the death of his second wife, Siobhán, early in 1591, Hugh O'Neill (qv), earl of Tyrone, protested his love for Mabel and asked for her hand in marriage. Bagenal temporised; O'Neill was importunate. Mabel was sent to live with her sister Lady Mary Barnewall at Turvey in north Co. Dublin, and Bagenal referred the decision to the authority of the queen and privy council of England, making it clear that he thought Mabel ill-prepared to live in the uncivil ambience of a Gaelic household. The potential advantage of the family connection to O'Neill was considerable and a number of prominent officials, including Secretary Fenton (qv) and Archbishop Loftus (qv), believed that the match would also be in the public interest. The decision was pre-empted by the couple, who pledged their troth when O'Neill visited Turvey in July, then eloped, and were married by the Church of Ireland bishop of Meath, Thomas Jones (qv), on 3 August, after he had assured himself of Mabel's free consent. Her infatuation is beyond doubt and it may be that O'Neill's judgment was impaired by love, as romanticists have supposed, but it seems more likely that he calculated that Bagenal would find it politic to accept the fait accompli.
Bagenal, however, remained implacably opposed and declared himself cursed ‘that my blood which in my father and myself hath often been spilled in repressing this rebellious race, should now be mingled with so traitorous a stock and kindred’ (quoted in Mac Carthy, 300 (spelling modernised)). He raised questions about the authenticity of O'Neill's divorce from his first wife, and withheld the dowry of £1,000 left to Mabel by her father, on the grounds that satisfactory jointure arrangements in the event of O'Neill's death had not been made. O'Neill, who assured Lord Burghley that it had been his intention that Mabel should bring civility to his house, encouraged her to furnish his castle at Dungannon in the English style, procured tapestries and paintings in London, and consulted Burghley on the choice of an architect to advise on a new country house.
Little is known of Mabel's adjustment to her new condition of life: she converted to catholicism and was deeply distressed by her brother's disapproval, by the increasing enmity between him and her husband, and, reputedly, by O'Neill's infidelity. The marriage was childless and seems to have reached a major crisis in May 1593 when the couple quarrelled about the murder of Phelim mac Turlough O'Neill: ‘the countess clapping her hands together was sorry, as should seem, of that which happened, to whom the earl in English spoke with vehemency’ (ibid., 310). He never again allowed her to appear in public. She died in December 1595, shortly after O'Neill's defeat of Bagenal at Clontibret; whether in virtual imprisonment at Dungannon or in refuge at Newry is disputed.