St. John, Oliver (sĭnˈjən) [key], 1598?–1673, English politician. He married (1638) a cousin of Oliver Cromwell. In 1637–38 he was, by his brilliant defense of John Hampden in the ship money case, drawn into the opposition to Charles I. Although Charles appointed (1641) him solicitor general, St. John remained a conspicuous opposition leader in the Long Parliament, taking a leading part in the attainder (1641) of Thomas Wentworth, earl of Strafford. He supported Cromwell and the army against Parliament in 1647 and was made (1648) chief justice of common pleas. He refused to take part in the trial (1649) of Charles I. St. John was one of the commissioners who negotiated (1652) the union with Scotland. His friendship with Cromwell cooled during the Protectorate, and he cooperated with Gen. George Monck in effecting the Restoration (1660) of the monarchy. In his Case of Oliver St. John (1660) he denied complicity in the execution of Charles I and the establishment of the Commonwealth. He was punished only with exclusion from holding office. He lived abroad after 1662.