The Manchester Martyrs were hanged in Manchester, England, for involvement in a scheme to free two Irish nationalists from custody in which a police officer was killed.

The Manchester Martyrs were three Irish Republicans – William Philip Allen, Michael Larkin, and Michael O'Brien – who were hanged in 1867 following their conviction of murder after an attack on a police van in Manchester, England, in which a police officer was accidentally shot dead, an incident that was known at the time as the Manchester Outrages. The three men were members of the Irish Republican Brotherhood, also known as the Fenians, an organisation dedicated to ending British rule in Ireland, and were among a group of 30 to 40 Fenians who attacked a horse-drawn police van transporting two arrested leaders of the Brotherhood, Thomas J. Kelly and Timothy Deasy, to Belle Vue Gaol. Police Sergeant Charles Brett, travelling inside with the keys, was shot and killed while looking through the keyhole of the van as the attackers attempted to force the door open by shooting the lock.

Manchester is a city and metropolitan borough in Greater Manchester, England. It had an estimated population of 568,996 in 2022. Greater Manchester is the third-most populous metropolitan area in the United Kingdom, with a population of 2.92 million, and the largest in Northern England. It borders the Cheshire Plain to the south, the Pennines to the north and east, and the neighbouring city of Salford to the west. The city borders the boroughs of Trafford, Stockport, Tameside, Oldham, Rochdale, Bury and Salford.

Irish nationalism is a nationalist political movement which, in its broadest sense, asserts that the people of Ireland should govern Ireland as a sovereign state. Since the mid-19th century, Irish nationalism has largely taken the form of cultural nationalism based on the principles of national self-determination and popular sovereignty. Irish nationalists during the 18th, 19th, and 20th centuries such as the United Irishmen in the 1790s, Young Irelanders in the 1840s, the Fenian Brotherhood during the 1880s, Fianna Fáil in the 1920s, and Sinn Féin styled themselves in various ways after French left-wing radicalism and republicanism. Irish nationalism celebrates the culture of Ireland, especially the Irish language, literature, music, and sports. It grew more potent during the period in which all of Ireland was part of the United Kingdom, which led to most of the island gaining independence from the UK in 1922.