Butler, Thomas (1634–80), earl of Ossory , lord deputy of Ireland, was born 8 or 9 July 1634 at Kilkenny, the second, but eldest surviving, son, of the eight sons and two daughters of James Butler (qv), 12th earl and 1st duke of Ormond, and his wife, Elizabeth (qv), Baroness Dingwall, only daughter of Richard and Elizabeth Preston (qv), earl and countess of Desmond. With his father an exile, he lived in France 1648–52, attending a Paris academy in 1649–50, in England 1652–7, where he was imprisoned in the Tower of London from March to October 1655 as an alleged royalist sympathiser, and in the Low Countries 1657–60. On 7 November 1659 he married Emilia (or Amilia), daughter of the Dutch nobleman Lodewyk van Nassau, Heer van Beverweerd (or Beverwart), and his wife, Elizabeth, daughter of Graaf van Horn; they had five sons and six daughters. Already by 1659 he had acquired a reputation for extravagance which would dog him thereafter, latterly exceeded by his notoriety for gambling.
Butler returned to England at the restoration. He, his father and his brother Richard Butler (qv), later earl of Arran, were admitted to Gray's Inn on 14 November 1660, and he participated in the coronation of Charles II in April 1661. He was elected to the English house of commons for Bristol on 16 May 1661, but he was not an especially active MP, particularly after the first session of the Cavalier parliament. Instead he acquired a series of posts in Ireland. In December 1660 he was appointed to the Irish privy council and from 1661 he held various Irish military commands, including that of lieutenant-general of the horse from 19 June 1661 and lieutenant-general of the army, for life, from 16 August 1665. He was elected an MP for Dublin University in 1661, but was called to the Irish house of lords as earl of Ossory on 8 August 1662. On 6 May 1664 he was named lord deputy of Ireland, and was sworn in on 21 May, deputising for his father, the lord lieutenant, during the latter's absence in England, until 3 September 1665. Over the next several years father and son would alternate in governing from Dublin or defending the Ormond interest at Whitehall and Westminster. His term of office was quiet, though he and the Irish council worried about the possible impact of legislation being considered in England to restrict the importation of Irish cattle.
This was an issue he raised upon his return to England, where he was appointed to the English privy council in June 1666, and named a gentleman of the bedchamber that year. On 14 September 1666 he was called to the English house of lords as Baron Butler of Moore Park (his father's Hertfordshire property). A lasting political alignment with the earl of Arlington, the powerful secretary of state, was strengthened by Arlington's marriage to the sister of Ossory's wife, but he quarrelled violently with his father's opponents Buckingham and Ashley, and was briefly confined in the Tower for breach of house of lords privilege (October–November 1666), resulting from a dispute with Buckingham arising from the cattle bill. He was awarded a DCL from Oxford University on 4 February 1667. He was named again as deputy on 7 February 1668, and was sworn in on 25 April, while his father again travelled to England; he remained deputy until the arrival, on 18 September 1669, of his father's successor, Lord Robartes (qv). As deputy he opposed the plans of Lord Orrery (qv) for Irish retrenchment, especially army cuts, which were seen as a subordination of Irish needs to the priorities of Whitehall.
In October 1670 he travelled to the United Provinces to escort Prince William of Orange (qv) to England, and became one of William's closest friends thereafter; in 1672 he acted as an envoy to France. He was instituted KG 25 October 1672, an honour shared with his father. He opposed the outbreak of war with the Netherlands in 1672, but served with distinction at sea, as he had, briefly, in the earlier conflict with the Dutch in 1666. He was commissioned a naval captain in 1672, rear-admiral 17 May 1673 and acted as vice-admiral from August, even holding overall command of the fleet for six days in September 1673. He was elected a brother of Trinity House 26 March 1673, and he acted as master from May 1675 to May 1676; he served as an admiralty commissioner 1675–9. In 1674 and 1677 he was involved in diplomatic negotiations with the Dutch and soon afterwards joined William on campaign, holding command of British forces in Dutch service from February to September 1678.
In the late 1670s he was active in English parliamentary politics on Ormond's behalf, and defended the queen, for whom he had been appointed lord chamberlain on 18 November 1676, during the ‘popish plot’. Whig successes in 1679 saw him lose his place on the English privy council, and he was suggested as an envoy to Spain in September 1679, but he was not sent. He was restored to the English privy council in April 1680, and in July 1680 he was appointed military governor of Tangier, an appointment he resented, given the inadequate resources assigned to the post. He died of fever on 30 July 1680 in London, before he could take up his Tangier command. He was survived by four of his daughters and two of his sons, James (qv), later 2nd duke of Ormond, and Charles (qv), later 2nd earl of Arran. His character impressed itself forcefully and favourably upon contemporaries and his popularity seems to have been genuine. A portrait is held by the National Portrait Gallery, London.