The Rump Parliament, which was the remnant of the Long Parliament following Pride's Purge, took the unprecedented step of charging King Charles I with treason. This act was rooted in the culmination of political tensions from the English Civil War, where loyalists and Parliamentarians clashed over governance and authority. The trial began in Westminster Hall, an iconic location steeped in legal history, on the premise that the king's military actions against his own subjects were grounds for treason.

This trial, held from late 1648 into early 1649, was fueled by a desire for accountability and to challenge the divine right of kings. A special court was established to hear the charges, questioning whether a monarch had the right to wage war against Parliament, which represented the people's will. High-profile figures, including Sir Henry Vane and Oliver Cromwell, played key roles in the events leading up to this trial. The parliamentarians believed that holding the king accountable would redefine the relationship between the monarchy and the people.

Charles I, maintaining his royal prerogative, refused to recognize the legality of the court, arguing that it was beneath his dignity. Nevertheless, the Rump Parliament pressed on, reflecting the growing power and assertion of Parliament over the monarchy. The trial brought significant challenges to the tradition of monarchy in England, setting the stage for the eventual rise of republicanism and the establishment of interim governance without a king.