Bradshaw, the son of a country gentleman, became a lawyer and in 1643 was appointed judge of the sheriff 's court in London. During the early years of the English Civil Wars, he used his legal talents to aid the Parliamentarians' cause. He became chief justice of Chester, Cheshire, in 1647, and in January 1649 the Independents (radical Puritans), who controlled the House of Commons, made him president of the court assembled to try Charles for treason. Charles repeatedly refused to plead, though he sought to have his case heard before Parliament—a request denied by Bradshaw. Charles was convicted and executed (Jan. 30, 1649).

In March 1649 Bradshaw became president of the Council of State, the executive body of the Commonwealth. Following Oliver Cromwell's establishment of the Protectorate in 1653, Bradshaw openly expressed his dissatisfaction with the new government and retired from politics (1654). In May 1659, following the death of Cromwell and the abdication of Cromwell's son Richard, Bradshaw was again made a member of the Council of State, and in June he became commissioner of the great seal.