O'Connor Faly, Tadhg (d. 1588?), disputed lord of Offaly, was the son of Giollapadraig O'Connor Faly, a noble of Offaly. Nothing is known about his early life. His family and its followers had been excluded from holding land within the plantation of Offaly, and their marginalised position drew the young Tadhg into the company of Ruaidhri Óg O'More (qv) and Fiach O'Byrne (qv). The submission of Fiach and his father, Aodh O'Byrne (qv), at Castledermot on 30 September 1579 signalled the wider submission of the Leinster nobility, and within days Tadhg, with his cousin Conchobhar O'Connor Faly, Brian MacMurrough Kavanagh (qv), and the O'Mores, had also come to terms with the Dublin government. Tadhg maintained his attachment to the O'Byrne faction, in summer 1580, answering the O'Byrne call to arms and sharing in the victory over Sir Arthur Grey (qv) at Glenmalure on 25 August 1580. Thereafter the O'Connor Falys and some members of the O'Mores, MacGillapatricks, and O'Carrolls joined Sir John Fitzgerald (qv) of Desmond (d. c.1582) to attack the midland plantations throughout September. But by summer 1581 Tadhg had withdrawn, leaving his cousin Conchobhar O'Faly to aid the O'Byrnes’ apparently abandoned ally James Eustace (qv), 3rd Viscount Baltinglass.
In early 1582 O'Byrne again drew Tadhg into his plans for a war on the Dublin government, cementing the alliance by pledging to him the hand of a sister, the widow of Cathaoir Dubh Kavanagh of Clonmullen. The O'Connor Falys resumed their hostility to the English; in May they captured the hated Captain Humphrey Mackworth and flayed him alive. When news came that a Spanish fleet was on its way, O'Byrne repaired relations between the Kavanagh houses of Garryhill and St Mullins, alarming the Dublin government. He then brought his sister to Offaly in June for her marriage to Tadhg. The Spanish fleet never materialised. On 16 September Tadhg, Fiach MacHugh O'Byrne, and Aodh Dubh O'Byrne of Knockrath made their submissions in Dublin, and on 5 November Fiach and Tadhg went to Dublin with Muircheartach Óg MacMurrough (qv) of Garryhill and made formal submission before the lords justices; these acts of conformity, however, did nothing to allay the general mistrust of their sincerity.
After the November 1582 submission Tadhg became less receptive to O'Byrne, indicating that they may have fallen out; the Dublin government, eager to destroy O'Byrne's nexus in the midlands, took advantage of this cooling of relations to sow dissent among the O'Connor Falys, exploiting dynastic disputes between Tadhg and his cousin Conchobhar. By mid-1583 Tadhg had assumed a loyalist disposition, while Conchobhar remained close to O'Byrne. The struggle between the cousins came to a dramatic climax on 13 September 1583, when they travelled to Dublin to lay their grievances before the arbitration of the lords justices: each accused the other of high treason, thereby playing into the hands of the officials. Before packed galleries the pair fought in the courtyard of Dublin castle until Tadhg beheaded Conchobhar. By this means Tadhg won the lordship of the O'Connor Falys, and was rewarded by the government with a farm and a state pension. He was later recorded as being pardoned on 4 May 1588 for unspecified offences, probably related to the attempts of Sir John Perrot (qv), lord deputy of Ireland, to destroy O'Byrne at the time of the Spanish armada crisis; in a deposition of 1590, Perrot explained how he had detached many of O'Byrne's confederates, and in particular how he had exploited rifts between O'Byrne and Tadhg. Nothing further is recorded of Tadhg, indicating that he may have died shortly after the summer of 1588.