O'Connor Faly (Ó Conchobhair Failghe), Brian (d. 1517), lord of Uí Failghe (Offaly), was seemingly second son of Tadhg O’Connor Faly and perhaps of a sister of Thomas FitzGerald (qv), 7th earl of Kildare. Nothing is known of his early life or those of his brothers. During the late 1460s and early 1470s his father Tadhg had contested the kingship of Offaly with his brother and overlord Conn O’Connor Faly (qv). Tadhg's death from plague (1471) collapsed his rebellion, allowing Conn to cement his grip on the kingship; as a result, on Conn's death (autumn 1474) his son Cathaoir (qv) assumed the kingship unopposed. One reason for this peaceful succession may have been that Brian and his brothers were probably still just boys.
By 1493 serious divisions had emerged between Cathaoir and the sons of Tadhg, who, led by the eldest, Toirdhealbach O’Connor Faly, clearly seem to have shaken Cathaoir's rule over Offaly. Such was their pressure that he publicly executed Toirdhealbach by hanging him (1493), silencing their opposition for many years. In the years that followed they do not seem to have attempted to exploit Cathaoir's often tense relationship with Gerald FitzGerald (qv), 8th earl of Kildare. In 1511 Cathaoir crossed Kildare once too often, and the earl then turned to his cousins, the sons of Tadhg. In doing so, he seemingly gave them his protection and backed their assassination of Cathaoir; and with Kildare's support, Brian as his client was inaugurated as king of Úi Failghe that year. Throughout Brian's kingship he remained a loyal client of the Kildares in the midlands, appearing on lists of presents of horses and armour given by the 9th earl in 1513. However, Brian's reign was brief, as he died in early 1517. Kildare muscle ensured that Brian's brother An Calbhach O’Connor Faly (c.1464–1519/25?) was elected king of Offaly in his place. Nothing substantive can be discerned about An Calbhach's reign, as he seems to have either died naturally or been overthrown by the son of Cathaoir, Brian O’Connor Faly (qv) (c.1500–c.1560).