In 1504, he supported Ulick Fionn Burke against Gerald FitzGerald at the Battle of Knockdoe and was defeated.
In 1510, he defeated the forces of Gerald FitzGerald, who was invading Thomond with a large army, at Moin na m-brathar, near Limerick.
Toirdhealbhach Donn Ó Briain died in 1528 and was succeeded by his son, Conchobhar.
[2] Ó Briain married, firstly, Joan, daughter of Thomas Fitzmaurice, 8th Lord of Kerry.
He married, secondly Raghnailt (died 1486),[2] daughter of Seán mac Conmara.