That same year, he jointly commanded a Norman army along with Sir Geoffrey de Geneville, Justiciar of Ireland against the Irish clans of County Wicklow.

Thomas and Justiciar de Geneville's forces attacked the Irish at Glenmalure, but they were soundly defeated and suffered severe losses.

In 1276, Brian Ruad, the deposed King of Thomond appealed to Thomas for support to help him regain his kingdom from his great-nephew Toirrdelbach MacTaidg O' Brien, who had usurped the throne.

In return for his aid, Brian Ruad promised that Thomas would be allowed to colonise all the land between Athsollus in Quin and Limerick.

O'Brien escaped to Galway where he elicited the help of his cousin William de Burgh, and in 1277 together with the assistance from clans, MacNamara and O'Dea they defeated the combined forces of Thomas and Brian Ruad.

Thereafter until his death in 1306, Toirrdelbach MacTaidg O'Brien ruled as undisputed King of Thomond and Thomas had no choice but to accommodate him.

[9] A mid-18th century compilation known as the Dublin Annals of Inisfallen states that Thomas was killed in battle against Turlough son of Teige and others.