The High Court of Justice was the court established by the Rump Parliament to try King Charles I of England. This was an ad hoctribunal created specifically for the purpose of trying the king, although the name was used for subsequent courts.
After the first English Civil War, the parliamentarians accepted the premise that the King, although wrong, had been able to justify his fight, and that he would still be entitled to limited powers as King under a new constitutional settlement. By provoking the second Civil War even while defeated and in captivity, Charles was held responsible for unjustifiable bloodshed. The secret “Engagement” treaty with the Scots was considered particularly unpardonable; “a more prodigious treason”, said Oliver Cromwell, “than any that had been perfected before; because the former quarrel was that Englishmen might rule over one another; this to vassalize us to a foreign nation.” Cromwell up to this point had supported negotiations with the king but now rejected further negotiations.
In making war against Parliament, the king had caused the deaths of thousands. Estimated deaths from the first two English civil wars has been reported as 84,830 killed with estimates of another 100,000 dying from war-related disease. The population of England in 1650 was estimated at only 5.1 million, meaning that the war deaths totalled 3.6% of the population.

Following the second civil war, the New Model Army and the Independents in Parliament were determined that the King should be punished, but they did not command a majority. Parliament debated whether to return the King to power and those who still supported Charles’s place on the throne, mainly Presbyterians, tried once more to negotiate with him.
The role of Parliament in ending a reign
Neither the involvement of Parliament in ending a reign nor the idea of trying a monarch was entirely novel. Parliament had asked for the abdication of Edward II (r. 1307–1327) who was charged with incompetence. Parliament also accepted the resignation of Richard II. However, in both these cases, Parliament acted at the behest of the new monarch. Parliament had established a regency council for Henry VI, although this was at the instigation of senior noblemen and Parliament claimed to be acting in the King’s name.
In the case of Lady Jane Grey, Parliament rescinded her proclamation as queen. She was subsequently tried, convicted and executed for high treason, but she was not brought to trial while still a reigning monarch.
Establishing the court
After the King had been moved to London, the Rump Parliament passed a Bill setting up what was described as a High Court of Justice in order to try Charles I for high treason in the name of the people of England. The bill initially nominated 3 judges and 150 commissioners, but following opposition in the House of Lords, the judges and members of the Lords were removed. When the trial began, there were 135 commissioners who were empowered to try the King, but only 68 would ever sit in judgement. The Solicitor General John Cook was appointed prosecutor.
Charles was accused of treason against England by using his power to pursue his personal interest rather than the good of England. The charge against Charles I stated that the king, “for accomplishment of such his designs, and for the protecting of himself and his adherents in his and their wicked practices, to the same ends hath traitorously and maliciously levied war against the present Parliament, and the people therein represented”, that the “wicked designs, wars, and evil practices of him, the said Charles Stuart, have been, and are carried on for the advancement and upholding of a personal interest of will, power, and pretended prerogative to himself and his family, against the public interest, common right, liberty, justice, and peace of the people of this nation.” The indictment held him “guilty of all the treasons, murders, rapines, burnings, spoils, desolations, damages and mischiefs to this nation, acted and committed in the said wars, or occasioned thereby.”

Although the House of Lords refused to pass the bill and the Royal Assent naturally was lacking, the Rump Parliament referred to the ordinance as an “Act” and pressed on with the trial anyway. The intention to place the King on trial was re-affirmed on January 6 by a vote of 29 to 26 with An Act of the Commons Assembled in Parliament. At the same time, the number of commissioners was reduced to 135 – any twenty of whom would form a quorum when the judges, members of the House of Lords and others who might be sympathetic to the King were removed.
The trial began on January 20, 1649 in Westminster Hall, with a moment of high drama. After the proceedings were declared open, Solicitor General John Cook rose to announce the indictment; standing immediately to the right of the King, he began to speak, but he had uttered only a few words when Charles attempted to stop him by tapping him sharply on the shoulder with his cane and ordering him to “Hold”. Cook ignored this and continued, so Charles poked him a second time and rose to speak; despite this, Cook continued. At this point Charles, incensed at being thus ignored, struck Cook across the shoulder so forcefully that the ornate silver tip of the cane broke off, rolled down Cook’s gown and clattered onto the floor between them. With nobody willing to pick it up for him, Charles had to stoop down to retrieve it himself.
When given the opportunity to speak, Charles refused to enter a plea, claiming that no court had jurisdiction over a monarch. He believed that his own authority to rule had been due to the divine right of kings given to him by God, and by the traditions and laws of England when he was crowned and anointed, and that the power wielded by those trying him was simply that of force of arfter Charles insisted that the trial was illegal, explaining, “No learned lawyer will affirm that an impeachment can lie against the King … one of their maxims is, that the King can do no wrong.” Charles asked “I would know by what power I am called hither. I would know by what authority, I mean lawful [authority].” Charles maintained that the House of Commons on its own could not try anybody, and so he refused to plead. The court challenged the doctrine of sovereign immunity and proposed that “the King of England was not a person, but an office whose every occupant was entrusted with a limited power to govern ‘by and according to the laws of the land and not otherwise’.