As the eldest living son he was the heir apparent and was styled with the corresponding courtesy title, which at first was Viscount Thurles, but changed to Earl of Ossory when his father was elevated to the marquessate in 1642. His early years were spent in Ireland until 1647 when he accompanied his father to England. As in 1648 his father renewed his support for the royalist cause, Lady Ormond moved to Caen, France, where she arrived on 23 June 1648 with her children. Ossory was an accomplished athlete and a good scholar. Having come to London in 1652 he was rightly suspected of sympathising with the exiled royalists, and in 1655 was jailed by Oliver Cromwell. After his release about a year later he went into exile to the Netherlands where Charles II had his exile court at the time.
Charles, became the de jure 3rd Duke of Ormonde, following his elder brother's attainder in 1715.
He accompanied Charles II back to England in 1660. In 1661 Ossory became a member of both the English and the Irish Houses of Commons, representing Bristol in the former and Dublin University in the latter.
Writ of acceleration
In 1662 he was called to the Irish House of Lords under a writ of acceleration as Earl of Ossory. His father held the title "5th Earl of Ossory" as one of his subsidiary titles. The acceleration made Thomas Butler the 6th Earl of Ossory. This was the only substantive title he ever held, as he would predecease his father and therefore never inherit his father's titles. His eldest son would later be the 2nd Duke of Ormond and the 7th Earl of Ossory.
Military career
Lord Ossory held several military appointments;
lieutenant-general of the army in Ireland
created an English peer as Lord Butler. Almost as soon as he appeared in the House of Lords he was imprisoned for two days for challenging the Duke of Buckingham.
Lord of the Bedchamber to Charles II, a post he held until his death.
In 1665 a fortunate accident allowed Ossory to take part in the Battle of Lowestoft against the Dutch, and in May 1672, being now in command of a ship, he fought against the same enemies in the Battle of Solebay, serving with great distinction on both occasions. The earl was partly responsible for this latter struggle, as on 12 March 1672, before war was declared, he had attacked the Dutch Smyrna fleet, an action which he is said to have greatly regretted later in life. Whilst visiting France in 1672 he rejected the liberal offers made by Louis XIV to induce him to enter the service of France, and returning to England he added to his high reputation by his conduct during the Battle of Texel in August 1673. From 1677 until 1679, he served alongside his father as a Lord of the Admiralty. Ossory was intimate with William, Prince of Orange, and in 1677 he joined the allied army in the Netherlands, commanding the British contingent and winning great fame at the siege of Mons in 1678. He acted as deputy for his father, who was lord-lieutenant of Ireland, and in parliament he defended Ormond's Irish administration with great vigour. In 1680 he was appointed governor of English Tangier, but his death prevented him from taking up his new duties. One of his most intimate friends was John Evelyn, who eulogised him in his Diary.
Death and succession
Ossory died on 30 July 1680.| !colspan=3|Timeline !align="left"|Age!!align="left"|Date!!align="left"|Event