Thomas was a grandson of John Treacy and one of six sons born to Thomas Treacy and Mary Carey/Carew of Soloheadbeg, Co. Tipperary. Of the six boys, only Thomas had children; two of his brothers, both named John, seem to have died very young, Edmund and Timmy never married, and Martin married but had no children.

This photo of Ellen O'Sullivan and Thomas was taken on their wedding day in 1915. They had four children, the eldest of whom died as an infant.

Thomas was manager, and later owner, of the gasworks in Carrick-on-Suir, Co. Tipperary. He died on 13 April 1969, his 88th birthday.