Ó Ciardhubháin is said to have been a native of Dunbally castle, near Dunmore, County Galway.
He had a quarrel with Thomas III de Bermingham, Ó Cellaigh of Áth Liag and other local families which forced him and his family to flee to the town of Galway, leaving the de Berminghams to possess their property.
A variant tradition states that: ... shortly afterwards he was reinstated in the possession of the castle & lands in consequence of an intermarriage that took place between Thomas Oge Mc Jarvis, his Lordship's fourth son, and Unagh Ní Ciorovane, and that the family remained there until 1625, when the lands were seized (that is, were taken possession of legally) by Richard Bermingham, 14th Lord Athenry, and afterwards vested in his son, Moiler Boy Bermingham of Dunmore.
However the means, Ó Ciardhubháin, with his family and followers, are stated in the city archives to have settled in the town in 1488, "where he became one of the principal, influential men then in Galway."
The family, while always acknowledged as of Gaelic origin, eventually rendered their surname from Ó Ciardhubháin to Kirwan.