In 1848, as editor of his own journal, United Irishman, he was convicted of seditious libel and sentenced to 14-years penal transportation for advocating James Fintan Lalor's programme of co-ordinated resistance to landlords and to the continued shipment of harvests to England.

In his last year, 1875, and while still resident in the United States, Mitchel was elected twice to the British Parliament from Tipperary on a platform of Irish Home Rule, tenant rights and free education.

In Newry, Mitchel attended a school kept by a Dr Henderson whose encouragement and support laid the foundation for classical scholarship that at age 15 gained him entry to Trinity College, Dublin.

[4] One of Mitchel's first steps into Irish politics was to face down threats of Orange Order retaliation by helping arrange, in September 1839, a public dinner in Newry for Daniel O'Connell.

But he also argued that religion is integral to education; that "all subjects of human knowledge and speculation (except abstract science)--and history most of all--are necessarily regarded from either a Catholic or a Protestant point of view, and cannot be understood or conceived at all if looked at from either, or from both".

[11] On 14 February 1846 Mitchel wrote again of the consequences of the previous autumn's potato crop losses, condemning the Government's inadequate response, and questioning whether it recognised that millions of people in Ireland who would soon have nothing to eat.

[17][18] When the London journal the Standard observed that the new Irish railways could be used to transport government troops to quickly curb agrarian unrest, Mitchel responded that the tracks could be turned into pikes and trains ambushed.

Mitchel had fallen under the influence of Scottish essayist, historian and philosopher Thomas Carlyle, a High Tory notorious for his antipathy toward liberal notions of enlightenment and progress.

"[24] It embraced views which Carlyle had espoused in On Heroes, Hero-Worship, & the Heroic in History (1841) and denounced British rule in Ireland, perceiving it to be suppressing Irish culture "in the name of Civilisation".

Duffy found that he had lent a journal, "recognised throughout the world as the mouthpiece of Irish rights", to "the monstrous task of applauding negro slavery and of denouncing the emancipation of the Jews,"[28][29] another of O'Connell's liberal causes against which Mitchel stood with Carlyle.

He later explained that he had come to regard as "absolutely necessary a more vigorous policy against the English Government than that which William Smith O'Brien, Charles Gavan Duffy and other Young Ireland leaders were willing to pursue".

He "had watched the progress of the famine policy of the Government, and could see nothing in it but a machinery, deliberately devised, and skilfully worked, for the entire subjugation of the island—the slaughter of portion of the people, and the pauperization of the rest," and he had therefore "come to the conclusion that the whole system ought to be met with resistance at every point.

Irish landlordism has made a covenant with British government in these terms—"Keep down for me my tenantry, my peasantry, my 'masses' in due submission with your troops and laws, and I will garrison the island for you and hold it as your liege-man and vassal for ever.

"[41]While decrying the "fatal cant of moral force",[42] and admitting no principle that distinguished his position from the "conspirators of Ninety-Eight" (the original United Irishmen), Mitchel emphasised that he was not recommending "an immediate insurrection": in the "present broken and divided condition" of the country "the people would be butchered".

The people should "obstruct and render impossible the transport and shipment of Irish provisions" and, by intimidation, suppress bidding for grain or cattle if brought "to auction under distress"—a method that had demonstrated its effectiveness in the Tithe War.

The Prospectus announced that as editor Mitchel would be "aided by Thomas Devin Reilly, John Martin of Loughorne and other competent contributors" who were likewise convinced that "Ireland really and truly wants to be freed from English dominion.

When the cases against O'Brien and Meagher fell through, thanks in part to Isaac Butt's able defence, under new legislation the government replaced the charges against Mitchel with Treason Felony punishable by transportation for life.

Once the Nautilus reached the Cape it was refused docking or supply during the convict crisis of 1849 and remained anchored off the coast for 5 months before sailing on to the penal colony of Van Diemen's Land (modern-day Tasmania, Australia)[53] to which O'Brien, Martin, Meagher, and other Young Irelanders, had been transported in the wake of their abortive July 1848 rising.

In Dublin, the Irish Confederation convened an emergency meeting to protest reports in American and British press outlets which "erroneously attributed" Mitchel's proslavery thought "to the Young Ireland party".

[64] In correspondence with his friend, the Roman Catholic priest John Kenyon, Mitchel revealed his wish to make the people of the US "proud and fond of [slavery] as a national institution, and [to] advocate its extension by re-opening the trade in Negroes".

After the secession from the American Union of several Southern states in February 1861 and the bombardment of Fort Sumter (during which his son John commanded a South Carolina battery), Mitchel was anxious to return.

As the South's manpower reserves depleted, Generals Robert E. Lee and Patrick Cleburne (a native of County Cork) proposed that slaves should be offered their freedom in return for military service.

If it be true that the state of slavery keeps these people depressed below the condition to which they could develop their nature, their intelligence, and their capacity for enjoyment, and what we call "progress" then every hour of their bondage for generations is a black stain upon the white race.

After the war a Union officer who claimed to have "loved John Mitchel, the Irish patriot, with a purer devotion" than any in Ireland, reported to a Boston paper that, as prisoners in Richmond, he and a fellow Irishman contacted his former idol.

That same year, his continued defence of southern secession caused him to be arrested in the offices of the paper and interned at Fort Monroe, Virginia, where Jefferson Davis and Senator Clement Claiborne Clay (accused of conspiracy to assassinate Lincoln) were the only other prisoners.

Mitchel, a "miserable man", was the proponent of a "diabolical" Democratic Party plan to impose upon blacks in the South, "as a substitute for chattel slavery, a system of serfdom scarcely less hateful than the institution it is intended to practically prolong".

Neither paper was in sympathy with the ethnic-minority Catholicism powerfully represented by the city's Tammany Hall Democratic-Party political machine and, until his death in 1864, by the authority of a third Ulsterman, Archbishop John Hughes.

[83] But, like Mitchel, Hughes had suggested that the conditions of "starving laborers" in the North were often worse than that of slaves in the South,[84] and in 1842 he had urged his flock not to sign O'Connell's abolitionist petition ("An Address of the People of Ireland to their Countrymen and Countrywomen in America") which he regarded as unnecessarily provocative.

[85] Back in New York City on 8 December 1874, Mitchel lectured on "Ireland Revisited" at the Cooper Institute, an event organised by the Clan-na-Gael and attended by among other prominent nationalists Jeremiah O'Donovan Rossa.

[96] Comparing him to Thomas Davis, W. B. Yeats concluded that a "harsh Ulster character, made hasher still by the tragedy of the famine, and the rhetoric of Carlyle" had a political influence that was "almost wholly mischievous".