Born the son of Irish immigrants in Cincinnati, Ohio (although other accounts claim he emigrated with his parents to Detroit, Michigan at the age of 3), Mackey served in the American Civil War and later became involved in the Irish nationalist movement.
Travelling to Ireland to take part in the Fenian Rising in 1865, he was arrested by British authorities in Cork and ordered to leave the country along with John McCafferty. However, upon his return two years later, he and James X. O"Brien participated in the capture of the Ballyknockane Constabulary barracks. He also briefly captured and held the Monning Martello tower near Fota Island in Cork Harbour.
This tower is believed to have been the only Martello tower ever captured.
After the rebellion"s end, he continued raiding gunshops and coastguard stations throughout Cork for over twelve months before his eventual capture by authorities on February 7, 1868. Tried for murder and treasonous felony, he was sentenced to twelve years penal servitude on March 21, 1868.
While imprisoned in Millbank Prison, he became acquainted with John Devoy. He was released under a general amnesty in 1871 on condition that he return to his native country.
Upon his return to the United States, he settled in Detroit, Michigan and opened a book and stationery store.
However, as a wave of dynamite bombings occurred in Great Britain during early 1881, he and Devoy would correspond with each other both condemning Rossa"s actions and the idea for a "bloodless revolution" in Ireland.
Irish Republican Brotherhood]
A later member of the American Land League, he became involved in the Clan na Gael and had been in France to make a withdrawal from the treasury of the Irish Republican Brotherhood from which he was to return to Ireland to plan for a possible rebellion with Devoy.
