[6] He began his education at Felsted School, whose pupils included four sons of Oliver Cromwell, and was supervised by Samuel Wharton, a "godly" minister appointed by the devoutly Puritan Earl of Warwick.

The loss of this region destroyed the Royalist army as a viable military force, and when the war ended with the Third Siege of Oxford in June 1646, Sir Thomas Fairfax appointed Rich one of the commissioners who negotiated its surrender.

[14] However, when Parliament tried to disband the New Model without settling their pay arrears, he supported his regiment's refusal to comply and helped draft the Heads of Proposals, which set out the army's conditions for a peace settlement with Charles I.

[1] After a series of disturbances in the City of London, in January 1648, Rich's regiment was based in the Royal Mews to guard Parliament and put down a pro-Royalist riot in April, just after the outbreak of the Second English Civil War.

In December 1648, Pride's Purge excluded MPs considered opponents of the army like Denzil Holles, creating a reduced body of 210 known as the Rump Parliament, most of whom were in favour of putting the king on trial.

[d] Although Rich supported the creation of the Commonwealth of England, he doubted the legality of the High Court of Justice for the trial of Charles I and refused to sit on it, while he did not take his seat in Parliament until February 1649, after the king's execution in January.

He benefitted from his new status by acquiring estates confiscated from the crown near Eltham Palace in Kent and High Easter in Essex,[1] and played a prominent role in supporting the army in Parliament.

[19] Like other Fifth Monarchists such as Major Generals Thomas Harrison and Robert Overton, Rich supported its replacement by the nominated "Barebones Parliament" in July 1653, but broke with Cromwell when he dissolved this body in December and became Lord Protector.

[1] It has been suggested he was viewed as a serious threat to the state, given his military connections and the influence of the Rich family in Essex and Suffolk, with several of the MPs who were permitted to take their seats linked to him or his relative, the Earl of Warwick.

[21] Cromwell's death in September 1658 and the succession of his son Richard led to a power struggle between the army and the Third Protectorate Parliament, which was dominated by crypto-Royalists and moderate Presbyterians similar to those excluded in December 1648.

Realising Monck intended to restore the monarchy, Rich supported John Lambert's attempt to maintain the Commonwealth by force, but his troops refused to follow him; Sir Richard Ingoldsby was appointed colonel in his stead and he was placed under arrest.