Thomas Butler, Viscount Thurles, drowns on December 15, 1619, off the coast of The Skerries, Isle of Anglesey. He is the son and heir apparent of Walter Butler, 11th Earl of Ormond (1559–1633), whom he predeceases. He resides at Thurles Castle, Thurles, County Tipperary. He is the father of the Irish statesman and Royalist commander James Butler, 1st Duke of Ormond.

Butler is born the eldest son of Walter Butler and his wife Helen Butler. His father is the 11th Earl of Ormond. His mother is the eldest daughter of Edmund Butler, 2nd Viscount Mountgarret and his wife Grizel FitzPatrick. His father and mother are cousins. Their common great-grandfather is Piers Butler, 8th Earl of Ormond. Their family, the Butler dynasty, is Old English and descends from Theobald Walter, who had been appointed Chief Butler of Ireland by King Henry II of England in 1177.

Some time before 1610, Butler marries Elizabeth Poyntz against his father’s wishes. She is the daughter of Sir John Pointz (died 1633) of Iron Acton in Gloucestershire and his wife Elizabeth Sydenham. He and Elizabeth had seven children, three sons and four daughters:

• James (1610–1688), became the 1st Duke of Ormond
• John (died 1636), died unmarried in Naples on his travels
• Richard (1615–1701), owned Kilcash, Garryricken, and other lands in the counties of Tipperary and Kilkenny
• Helena or Ellen or Eleanor (1612–1682), married Donough MacCarty, 1st Earl of Clancarty
• Eleanor or Ellen, marries Sir Andrew Aylmer, baronet, of Donadea in County Kildare
• Mary (died 1680), marries Sir George Hamilton, 1st Baronet, of Donalong
• Elizabeth (died 1675), marries first James Purcell, Baron of Loughmoe, by whom she has Nicholas Purcell of Loughmoe; she marries secondly John FitzPatrick

In 1619 after the beginning of his father’s long imprisonment in the Fleet Prison, Butler is summoned to England to answer charges of treason, specifically, of having garrisoned Kilkenny. However, on December 15 the ship conveying him is wrecked off the coast of The Skerries, Isle of Anglesey and he drowns. Like his father, he is a prominent Catholic and it seems likely that his refusal to conform to the established Anglican religion had angered King James I, and may have been the true motive for his summons.

Butler predeceases his father who dies in 1634. His eldest son James, the future 1st Duke of Ormond, succeeds him as heir apparent and bearer of the courtesy title Viscount Thurles until he succeeds his grandfather as the 12th Earl of Ormond.