Born at Oxford, he was the eldest son of Sir Henry Marten, a lawyer and magistrate who owned lands in Berkshire and Oxfordshire. Marten was educated at University College, Oxford, and the Inner Temple. He married twice during the 1630s. His second wife, Margaret, outlived him, but Marten gained an enduring reputation as a womaniser and a drunkard — King Charles I is said to have ordered him to leave a race meeting at Hyde Park because his very presence was offensive.
Marten was elected to the Short and Long Parliaments as MP for Berkshire, where he came to be known both for his radical views and for his ready wit. He was appointed to the Committee of Safety in July 1642. When the First Civil War broke out, Marten subscribed £1,200 to the parliamentary cause and raised a regiment of horse. He did not go to the wars, but became infamous as one of the first to call openly for the overthrow of the monarchy and the establishment of a republic. In August 1643, he was expelled from Parliament and imprisoned in the Tower of London for saying that the destruction of one family — the royal family — was preferable to the destruction of many families. Marten was released from imprisonment after two weeks, but he was not allowed to resume his seat in Parliament for three years. He took command of a troop in the Berkshire Trained Bands and was appointed governor of Aylesbury in May 1644. During the winter of 1645-6, he was with Colonel Dalbier at the siege of Donnington Castle in Berkshire.
In July 1646, Marten was re-elected MP for Berkshire. He became a close political ally of Thomas Chaloner, and joined him in questioning the entitlement of the Scots to involvement in the peace negotiations with the King. Marten was instrumental in passing the Vote of No Addresses in January 1648, which attempted to break off negotiations and push through a settlement on Parliament's terms. Marten supported the Levellers' constitutional proposals, and was the only MP to retain the trust of John Lilburne. During the Second Civil War (1648), Marten raised an unauthorised regiment in Berkshire. Described as a regiment of Levellers, Marten's troops proclaimed that they fought "for the people's freedom against all tyrants whatsoever". Marten marched his regiment around the Midlands independently of the Army command, but it was eventually incorporated into the New Model Army.
After the King's defeat, Marten played a leading role in the King's trial, helping to draft the charges against him and sitting as a member of the High Court of Justice. Marten and Cromwell famously flicked ink at one another during the signing of the King's death warrant.
Marten was a central figure in the establishment of the Commonwealth in 1649. He was a member of the committees that supervised the abolition of the Monarchy and the House of Lords, he supported Henry Ireton's proposal that the Oath of Engagement should include a clause indicating approval of the regicide, and he was appointed to the first Council of State. Regarded by some as an atheist, Marten described himself as a radical sceptic in religion. He opposed state control of the church, and argued for religious toleration — going so far as to oppose the invasion of Ireland on the grounds that the English could not seek religious freedom for themselves then try to impose a religious settlement on the Irish. Marten received grants of lands in recognition of his services to Parliament's cause, but these proved difficult to manage and contributed to the financial difficulties that plagued him during the 1650s.
In April 1653, Marten argued bitterly with Cromwell over the dissolution of the Purged Parliament, which brought the republican Commonwealth to an end. Cromwell singled Marten out for criticism during the speech he made at the dissolution, accusing him of being a drunkard and whoremaster — probably in reference to Marten's adulterous relationship with Mary Ward, who lived openly with him as his common-law wife, and with whom he had three daughters. Marten's financial problems kept him from gaining any great influence during the Protectorate. He briefly returned to Parliament when the Purged Parliament was recalled in 1659, but with little of his former influence.
At the Restoration, Marten made no attempt to escape and bravely defended his principles when he was brought to trial as a regicide in October 1660. His death sentence was commuted to life imprisonment, probably because he had protected Royalists during the 1650s. After short spells of imprisonment at Berwick and Windsor, he spent the rest of his life a prisoner under lenient conditions at Chepstow Castle, where he died in September 1680, having choked while eating his supper.
Reference:
John Aubrey, Brief Lives, ed. O.L. Dick, 1992
Sarah Barber, Henry Marten, Oxford DNB, 2004
C.H. Frith, Henry Marten, DNB, 1893