Charles I, the king of England, Scotland, and Ireland, was executed on Tuesday, 30 January 1649 outside the Banqueting House on Whitehall, London. The execution, carried out by beheading the king, was the culmination of political and military conflicts between the royalists and the parliamentarians in England during the English Civil War, leading to the capture and trial of Charles. On Saturday 27 January 1649, the parliamentarian High Court of Justice had declared Charles guilty of attempting to "uphold in himself an unlimited and tyrannical power to rule according to his will, and to overthrow the rights and liberties of the people" and he was sentenced to death by beheading.

King Charles the Martyr, or Charles, King and Martyr, is a title of Charles I, who was King of England, Scotland and Ireland from 1625 until his execution on 30 January 1649. The title is used by high church Anglicans who regard Charles's execution as a martyrdom. His feast day in the Anglican calendar of saints is 30 January, the anniversary of his execution in 1649. The cult of Charles the Martyr was historically popular with Tories. The observance was one of several "state services" removed in 1859 from the Book of Common Prayer of the Church of England and the Church of Ireland. There remain some churches and parishes dedicated to Charles the Martyr, and his cult is maintained by some Anglo-Catholic societies, including the Society of King Charles the Martyr founded in 1894 and the Royal Martyr Church Union founded in 1906.