Keightley, Thomas (c.1650–1719), government official, was born in Hertfordshire, England, only son of William Keightley of Hertingfordbury, Hertfordshire, and his wife Anne, daughter of John Williams of London. In 1672 he was appointed gentleman-usher to James (qv), duke of York, which association was strengthened by Keightley's marriage (9 July 1675) to Frances, daughter of Edward Hyde, earl of Clarendon, and sister of York's first wife. Soon after his marriage Keightley sold his property in Hertfordshire and moved to Ireland, where he received a 31-year grant of £238 annual rents from York's Irish estate and a yearly pension of £400. The assumption that Keightley converted to catholicism around this time is based on the presence of several catholics in his extended family, and on Frances's conversion in the 1680s. However, in 1686 Frances's anglican brother, Henry Hyde (qv), earl of Clarendon, informed his younger brother, Laurence Hyde (qv), earl of Rochester, that he was satisfied with regard to Keightley's religion, thereby implying that the doubts expressed about Keightley's adherence to the protestant church were unfounded. In fact, it appears that Keightley's estrangement from his wife in the later 1680s, after the birth of seven sons and two daughters (of whom only a daughter, Catherine, survived to adulthood), was caused by Frances's conversion, an action that aroused active concern for her mental well-being in her two brothers. The marriage proved irreparable.
After Clarendon's appointment as lord lieutenant of Ireland, Keightley was appointed vice-treasurer (1686), though the grant applied only to the judicial role, with a annual salary of £20. Both Clarendon and Rochester hoped to get Keightley appointed to the revenue commission as well, though their endeavours during 1686–8 met without success. In July 1686 Clarendon sent Keightley to England in order to keep Rochester, then England's lord high treasurer, informed on Irish affairs. Keightley stayed in England for the remainder of James II's reign, being one of the last people to speak with the king before his departure for France (December 1688). Keightley had been sent by Clarendon to try to convince the king to remain in England.
Despite his involvement with government under James II, after the 1688 revolution Keightley became a central figure in Irish government for more than twenty years. In 1692 he was appointed to the privy council and revenue commission. He sat in the Irish parliament for Ennisteoge (Inistioge), Co. Kilkenny (1695–9), and Co. Kildare (1703–11, 1713–14), and was a consistent adherent of the court party. His parliamentary activity related mainly to revenue supply proceedings, and he was usually identified with the tories. In 1695 he was praised by the tory lord chancellor, Sir Charles Porter (qv), for his part in preventing the attempted impeachment of Porter by the whig lord deputy's parliamentary managers. The lord deputy, Henry, Lord Capel (qv), went so far as to describe Keightley as a Jacobite.
In the early 1690s Keightley was also involved in proceedings for recovery of his rents and pension, which had not been paid since 1689. Having tried for a renewal of the original grants, he petitioned (1694) for a custodiam out of the Williamite land forfeitures, initially receiving a three-year grant. Having received favourable rent remissions, he petitioned successfully for a lifelong grant. The 1699 report of the English-appointed parliamentary commissioners of inquiry into the forfeitures named Keightley as one of the sixteen grantees who benefited most from the forfeitures, and one of five grantees who had sold substantial parts of their grants. The resumption of the forfeitures by the English parliament in 1700 threatened to ruin Keightley financially, though in time he managed to get an act passed confirming his grant.
Keightley's position improved with the appointment of his tory brother-in-law, Rochester, as lord lieutenant (1700). Prior to Rochester's arrival (autumn 1701), Keightley acted as his personal agent, adviser, and mouthpiece in government. In return Rochester secured a regrant of Keightley's 1680s pension, along with a pension for his daughter, Catherine. After Rochester's return to England, Keightley was appointed as one of his lords justices (March 1702–February 1703). His high profile under Rochester led to an unfounded rumour that Keightley was to be made an earl and appointed lord deputy. Having taken a leading role in the preparations for the 1703 parliament convened by the new tory lord lieutenant, James Butler (qv), duke of Ormond, Keightley was involved in the court party's negotiations with the whigs regarding the revenue supply, and in the tory government's pre-session meetings for the 1705 session, while in 1707 he again took a leading role in the negotiations on supply, and, on the order of the lord lieutenant, Thomas Herbert (qv), earl of Pembroke, made the proposal in the house of commons for the compromise supply. In 1709, when the whigs were in government, Keightley sided with the court against the tories in the supply proceedings. The following year he again acted on behalf of the whig court party in parliament, and served as a commissioner of the great seal (November 1710–January 1711) after the death of the whig lord chancellor, Richard Freeman. However, Keightley was quick to express his pleasure at the return to tory government in 1711 under Ormond, while in the 1713–14 session he voted for Sir Richard Levinge (qv), the defeated tory candidate in the speakership contest. His association with the tories resulted in his removal from the revenue commission after the Hanoverian succession (1714). The year before, he had received a pension of £1,000. He did not serve in office again, and died on 19 January 1719.