Sir Robert Pye was son of Sir Robert Pye Senior (1585-1662) and his wife, Mary the daughter of John Croker of Batsford in Gloucestershire. His father became, by the favour of the Duke of Buckingham, Remembrancer of the Exchequer in July 1618, was knighted on 13th July 1621, bought the estate of  Faringdon House in Berkshire from the heirs of Sir Henry Unton in February 1623 (though didn't take possession until after 1631) and represented Woodstock in the Long Parliament. He contributed £1,000 towards the recovery of Ireland, remained at Westminster after the breach with the King and passed for a thoroughgoing supporter of the Parliament. In early life, says Ben Jonson, "he loved the Muses" and Jonson sent him, through John Burgess, a rhyming petition for the payment of the arrears of his pension.

Robert Junior, the son, married Anne the daughter of John Hampden, the famous parliamentarian, and his first wife, Elizabeth Pyrton, in 1642; and, in the same year, raised a troop of horse for the army of the Earl of Essex. In January 1643, a letter from the elder Pye to Sir Edward Nicholas was intercepted and read in the House of Commons, which proved that he was seeking to make his peace with the King and secretly contributing money for his service. The letter also stated that his son's conduct in taking arms against the King was done without his consent or knowledge, neither should he have any supplies of money from him. It was only through Hampden's influence that the writer escaped expulsion from the house.

The younger Pye was colonel of a regiment of horse under Essex during the Cornish Campaign of 1644 and, in June of that year, captured Taunton Castle. He was wounded at the taking of Cirencester in September 1643. In April 1645, he was appointed colonel of a regiment of horse in the New Model Army. In May 1645, he was sent to join Colonel Vermuyden and a body of horse who were to assist the Scottish army in the north of England; but, passing through Leicester on his way, he was persuaded to remain there to take part in its defence against the King. Pye showed much skill and courage during the defence, was taken prisoner when Leicester fell and was exchanged for Sir Henry Tillyer a few days later. He published an account of the siege, entitled 'A more exact Relation of the Siege laid to the town of Leicester . . . delivered to the House of Commons by Sir Robert Pye, Governor of the said Town, and Major James Ennis' (1645). The events of the siege caused a lively controversy and a number of tracts relating to it are reprinted by Nichols.

In September 1645, Pye took part in the Siege of Bristol and, in May 1646, he was detached by Fairfax to command the forces sent to besiege Faringdon, which surrendered, with Oxford, on 24th June 1646. He was one of the officers who undertook, in March 1647, to engage their men to serve in the expedition to Ireland; but his regiment mutinied and joined the rest of the army in their opposition to disbanding. Pye succeeded in bringing off a certain number of troopers. These - who formed part of the force collected by the city to resist the army in July 1647 - were regarded with special animosity by their late comrades. He was arrested by a party of the army in August 1647, but immediately released by Fairfax.

Pye eventually became reconciled to the Government of Cromwell and sat in the parliaments of 1654 and 1658 as member for Berkshire. In January 1660, he again came forward as an opponent of military rule and presented a petition for the re-admission of the secluded members. For this, the Parliament sent him to the Tower and, though he sued for a writ of habeas corpus at the upper bench, it was refused by Judge Newdigate. He was released on 21st February 1660. He represented Berkshire in the Convention Parliament of 1660, but took little part in politics afterwards, though he lived till 1701. He inherited the Faringdon estates in 1662 and, in December 1688, joined the Prince of Orange on his way to London.

By his marriage with Anne Hampden, Pye had four children, only two of which, Hampden and Edmund MD, appear to have lived to adulthood. The last was the great-grandfather of the laureate, Henry James Pye.

Edited from Leslie Stephens & Sidney Lee's "Dictionary of National Biography" (1891).