The Manchester Martyrs are hanged in Manchester, England, for killing a police officer while freeing two Irish Republican Brotherhood members from custody.

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.

The Irish Republican Brotherhood was a secret oath-bound fraternal organisation dedicated to the establishment of an "independent democratic republic" in Ireland between 1858 and 1924. Its counterpart in the United States of America and Canada was initially the Fenian Brotherhood, but from the 1870s it was Clan na Gael. The members of both wings of the movement are often referred to as "Fenians". The IRB played an important role in the history of Ireland, as the chief advocate of republicanism during the campaign for Ireland's independence from the United Kingdom, successor to movements such as the United Irishmen of the 1790s and the Young Irelanders of the 1840s.