In 1848 Mitchel established the United Irishman but was soon arrested and tried for his articles on a charge of treason. Found guilty, he was sentenced to 14 years' transportation. In 1853 he escaped from Van Diemen's Land (Tasmania) and made his way to the United States.
Mitchel worked as a journalist in America and established the newspaper, The Citizen. He also published several books including Jail Journey (1854) and the History of Ireland from the Treaty of Limerick (1868).
In 1874 John Mitchel returned to Ireland and the following year was elected to the House of Commons. However, he died before he could take his seat.
He would be a bad Irishman who voted for principles which jeopardized the present freedom of a nation of white men, for the vague forlorn hope of elevating blacks to a level for which it is at least problematical whether God and nature ever intended them.