In 1648, King Charles I was in captivity at Carisbrooke Castle and the English Civil War was over, bar a few pockets of royalist resistance across the country. The Long Parliament issued a set of demands for the future government of the Kingdom and sent commissioners to negotiate with the King. The leaders of the New Model Army had previously tried to negotiate with the King themselves in 1647, shortly after the end of the first civil war in 1646. Its leaders, the "grandees", were sorely disappointed when Charles stalled these negotiations by quite clearly attempting to play different factions in the Parliamentary alliance off against others. He eventually escaped captivity, leading to the second civil war that raged between 1647 and 1649. By the time Charles was recaptured, most of the army leaders were convinced that they could no longer trust him. So the army sent in a Remonstrance on 20 November 1648 which was rejected by 125 votes to 58 in the House of Commons on 1 December. When the Commissioners returned with the King's answers, which were far short of what was hoped, the House of Commons eventually declared them acceptable by 129 votes to 83 early in the morning of 5 December 1648 (though this was technically a vote on whether the vote should be called).
On Wednesday 6 December Col. Pride’s Regiment of Foot took up position on the stairs leading to the House, while Nathaniel Rich’s Regiment of Horse provided backup. Pride himself stood at the top of the stairs. As MPs arrived, he checked them against the list provided to him; Lord Grey of Groby helped to identify them. Of 489 MPs at the time, 18 were permanently absent before the purge. 45 were barred from Parliament and imprisoned. 186 were barred from Parliament but not imprisoned. 86 were not barred but absented themselves voluntarily. 83 were allowed back in Parliament after formally dissenting from the decision to accept the King's proposals. 71 were supporters of the army from the outset.
The imprisoned members were taken first to the Queen’s Court within the Palace of Westminster, and then to a nearby public house. There were three public houses next to the Palace in 1648, called Heaven, Purgatory, and Hell. The imprisoned members were taken to Hell where they spent the night. On the next day they were moved to two inns in the Strand. By 12 December the first of the imprisoned members was allowed home; many more were released on 20 December.
The purged House, later nicknamed the Rump Parliament by critics, now had a majority that would establish a Republic. Any doubts the remaining members may have had over the wisdom of this course was suppressed by the presence of the Army in great numbers. On 4 January 1649 an Ordinance was passed to try the King for treason; the House of Lords rejected it. The House of Commons then passed an ‘Act’ by itself for the same purpose, and the King was beheaded on 30 January. On 6 February the House of Lords was abolished; the monarchy went the same way on 7 February , and a Council of State established on 14 February.
Pride's Purge was arguably the most significant event of the English Civil War, directly leading to the execution of Charles I and thus a permanent end to hostilities between Crown and Parliament. Historians argue over the extent to which this was an independent action by Pride's regiment. Army chief Sir Thomas Fairfax and his second in command, Lieutenant-General Oliver Cromwell, stayed aloof from the proceedings. But Cromwell's swift journey to London from Pontefract on the day of the purge implies that he may have been involved in its planning. He most certainly benefited from and supported the outcome of the purge after it had taken place.