He entered Parliament in 1640 as a royalist supporter, but changed sides in 1643, eventually becoming a member of Cromwell’s council of state. In 1660 he was one of the Commissioners of the Convention Parliament who invited Charles II to return, and Charles rewarded him with the Chancellorship of the Exchequer. After Clarendon’s fall he became one of the cabal, but was dismissed in 1673 because of his support for the Test Act and his unwavering opposition to Roman Catholicism. He became leader of the opposition, and used the Popish Plot to try to exclude the Roman Catholic James, Duke of York, from the succession (the Exclusion Crisis), but his political failure led him to flee into exile in 1682.