King, Sir Robert (d. 1657), parliamentarian politician, was eldest son of Sir John King (qv) of Boyle Abbey, Co. Roscommon, and his wife Catherine, daughter of Robert Drury. King was educated at Cambridge, and on his return to Ireland in 1618 succeeded his father as muster-master-general. He was knighted in 1621, and worked with the Dublin administration for the next twenty years. Despite the early hostility of Viscount Wentworth (qv), King supported the government in the 1634 parliament, where he sat for the borough of Boyle. His willingness to return his impropriated church lands (with the encouragement of Bishop Bramhall (qv)) helped to change the lord deputy's mind, and in October 1637 he was confirmed in his position as muster-master with official approval. Reelected for Boyle in 1640, King took no part in the attack on Wentworth in the Irish parliament, but after the lord lieutenant's arrest (November) he joined the opposition, presumably to save his own skin. In 1641 he attended the Westminster parliament as a witness against the lord lieutenant, and provided information that was vital in bringing his master to the block.
At the outbreak of the Irish rebellion, King hastily returned to Roscommon, where he took part in the battle of Ballintubber (1642). In April 1643 he was back in London, and joined William Jephson (qv) and Arthur Hill (qv) on a committee that attended Charles I at Oxford, hoping to secure the royal assent for a new adventurers' act to provide funds for the Irish war. Charles's refusal pushed King into support for parliament. He took the Solemn League and Covenant in 1644 and was dismissed as muster-master by a furious Charles I in January 1645. In April King was appointed as one of parliament's Ulster commissioners, and travelled to Ireland to coordinate the English war effort with that of the Scottish army under Robert Monro (qv). From November 1645 he was at the centre of attempts to persuade the marquess of Ormond (qv) to abandon negotiations with the confederate catholics and throw in his lot with parliament. Despite some encouragement from Dublin, these talks failed in the spring of 1646, and Ormond went on to sign an agreement with the confederates in the summer. On the failure of this ‘Ormond peace’ (September), King was again chosen to negotiate with the king's lord lieutenant, and he was one of the commissioners who signed the Dublin articles, under which Ormond agreed to surrender the Leinster garrisons and leave the country. Unlike many at Westminster, King was not hostile to Ormond, and he maintained a private correspondence with the lord lieutenant during and after the formal negotiations. Indeed, King was never closely involved with any of the factions in London, and seems to have been mainly concerned with the fate of protestant Ireland throughout this period.
King supported parliament after the execution of Charles I, and advised Oliver Cromwell (qv) in the weeks before his invasion of Ireland in 1649. He was reappointed muster-master in November 1649, and on his return to Ireland in early 1651 became involved in the administration of the army, sharing responsibility for military pay in the province of Leinster with Col. John Hewson (d. 1662). From March 1652 he worked as an assistant to the parliamentary commissioners at Dublin, and sat on various commissions and committees in later years. The strength of his ties to the commonwealth regime became clear in 1653, when he was chosen to represent Ireland in the nominated assembly, and in November of that year he was appointed to the English council of state. King was also well respected in the Irish protestant community. In the early 1650s he arranged marriages for his children with the Basills, Cootes, Merediths, and Fentons, and he worked with Lord Broghill (qv) and Vincent Gookin (qv) in promoting Irish issues in England. In 1654, in an indication of his local standing in Connacht, he was elected for Sligo, Leitrim, and Roscommon for the Westminster parliament. He was returned for the same constituency in 1656. King travelled to England but was prevented by ill-health from playing a significant role in political affairs. He died in June 1657. King married first Frances, daughter of Lord Folliott of Ballyshannon; on her death he married (1638) Sophia, widow of Sir Edward Cecil, Viscount Wimbledon. His eldest son, Sir John King (qv), became 1st Baron Kingston in 1660.