Michael Barrett was born in 1841 in Drumnagreshial, near Ederney, in County Fermanagh, Ireland. Like many Irishmen of his generation, he grew up in the shadow of British colonial rule and the trauma of the Great Famine. As a young man, he left Ireland in search of work and relocated to Glasgow, Scotland.

At the age of 27, Barrett joined the Irish Republican Brotherhood (IRB), also known as the Fenians. The group was a militant nationalist organization advocating for the complete separation of Ireland from British rule. By the 1860s, the Fenians had become a significant force, boasting tens of thousands of members across both Ireland and Great Britain. Unlike more moderate Irish nationalist groups, the Fenians rejected compromise and called for direct action, including armed rebellion.

On 13 December 1867, a bomb was detonated outside the Middlesex House of Detention in Clerkenwell, London, in an attempt to break out Ricard O’Sullivan Burke, a senior Fenian imprisoned there. The bomb, intended to breach the prison wall, instead caused catastrophic damage to nearby tenement buildings. The explosion killed 12 innocent bystanders and wounded up to 120 more, many of them working-class Londoners.

The bombing shocked Britain and led to a sweeping crackdown on Irish radicals. Public sentiment quickly turned against the Fenians. Even sympathetic voices like Karl Marx and Charles Bradlaugh condemned the act, citing the indiscriminate violence and backlash it provoked. Prime Minister Benjamin Disraeli, who had just banned political demonstrations in London, benefited politically from the fallout, as the explosion seemed to justify his hardline stance.

Michael Barrett had been arrested months earlier in Glasgow for illegally discharging a firearm, but authorities soon tied him to the Clerkenwell incident. During his trial, Barrett maintained his innocence, stating that he was in Scotland at the time of the bombing. He brought forward witnesses to confirm his alibi.

The case against him relied heavily on the testimony of Patrick Mullany, a dubious witness with a history of false statements. Mullany claimed that Barrett had confessed to the bombing and named an accomplice called "Murphy." Mullany was later rewarded with a free passage to Australia, casting doubt on his credibility. Nevertheless, the jury took only two hours to reach a guilty verdict, and Barrett was sentenced to death.

Barrett’s final speech from the dock was both emotional and defiant. He acknowledged his deep love for Ireland and questioned the justice of his conviction. His words echoed throughout Irish nationalist circles: "I love my country, and if it is murderous to love Ireland dearer than I love my life, then it is true, I am a murderer."

Despite appeals for clemency, including from Radical MPs, writers, and his own elderly mother, who walked miles in the snow to plead his case, no pardon was granted.

On 26 May 1868, Michael Barrett was publicly hanged outside Newgate Prison in London, in front of a crowd of 2,000 people. The execution was rowdy; spectators reportedly jeered, booed, and sang songs like “Rule Britannia” and “Champagne Charlie” as the noose was tightened. The hangman was William Calcraft, notorious for botched executions.