On 11 May 1812, at about 5:15 pm, Spencer Perceval, the prime minister of the United Kingdom of Great Britain and Ireland, was shot dead in the lobby of the House of Commons by John Bellingham, a Liverpool merchant with a grievance against the government. Bellingham was detained and, four days after the murder, was tried, convicted and sentenced to death. He was hanged at Newgate Prison on 18 May, one week after the assassination and one month before the start of the War of 1812. Perceval remains the only British prime minister to date to have been assassinated.

Perceval had led the Tory government since 1809, during a critical phase of the Napoleonic Wars. His determination to prosecute the war using the harshest of measures caused widespread poverty and unrest on the home front; thus the news of his death was a cause of rejoicing in the worst-affected parts of the country. Despite initial fears that the assassination might be linked to a general uprising, it transpired that Bellingham had acted alone, protesting against the government's failure to compensate him for his treatment a few years previously when he had been imprisoned in Russia for a trading debt. Bellingham's lack of remorse, and apparent certainty that his action was justified, raised questions about his sanity, but at his trial he was judged to be legally responsible for his actions.After Perceval's death, Parliament made generous provision to his widow and children and approved the erection of monuments. Thereafter his ministry was soon forgotten, his policies reversed, and he is generally better known for the manner of his death than for any of his achievements. Later historians have characterised Bellingham's hasty trial and execution as contrary to the principles of justice. The possibility that he was acting within a conspiracy, on behalf of a consortium of Liverpool traders hostile to Perceval's economic policies, is the subject of a 2012 study.

John Bellingham (1769 – 18 May 1812) was an English merchant and perpetrator of the 1812 murder of Spencer Perceval, the only British prime minister to be assassinated.