O’Brien was charged with high treason and held at Kilmainham until two days before his trial began at Clonmel (Tipperary) on 21 September 1848. The redoubtable James Whiteside led his defence, arguing that the whole business had been no more than an attempt to evade arrest, an approach that tended to degrade the struggle for national liberation. O’Brien later described the ‘humiliation’ that this caused him and how he wished he could have ‘avowed’ and ‘justified’ all he had done. On 7 October, the jury found him guilty of high treason. He was sentenced to be hanged, drawn, beheaded and quartered, with the four quarters ‘dispersed as Her Majesty shall think fit’. But Home Secretary Grey knew it would be ‘a good thing if we can avoid hanging him without proclaiming impunity to future rebels, as the less we do to exalt him to the rank of a martyr the better’. The sentence would be commuted to transportation for life. Meagher, MacManus and O’Donohoe also had their death sentences commuted to transportation. The ‘poor Ballingarry men’ (about 20 peasants and colliers) were all released in November 1848.
The judicial appeals by O’Brien and his three companions were rejected by the Lords in May 1849 and he was expelled from Parliament as a convicted traitor. He was horrified by the thought of perpetual banishment, ‘16,000 miles from all whom I love’, and regretted that he ‘was not executed at Clonmel’. The commutation of the sentences to transportation was effected in spite of legal challenges from the defendants. On 9 July, the four men were taken from their prison and, with O’Brien’s face ‘bathed in tears’, despatched on the long journey to Van Diemen’s Land (Tasmania).
MacManus (1851), Meagher (1852), O’Donohoe (1852) and Mitchel (1853) all escaped to the United States. O’Brien’s attempted escape in 1850 failed and he remained in Van Diemen’s Land, distressed by the separation from home and family and troubled by bad health, until 1854. He was then given a conditional pardon, allowing him to travel to anywhere except the United Kingdom, and he chose to live in Brussels. In 1856, he was allowed to return to Ireland, where the Repeal cause had died. Having ‘lost all confidence in public men’, O’Brien chose not to involve himself in politics, bar the writing of the occasional public letter. He travelled widely and died outside Ireland, at Bangor in north Wales, on 18 June 1864.
For most of his career, though admirable in many ways, O’Brien did not have the political stature to dictate the political agenda, and he lacked the flexibility and finesse to excel as an opportunist. Only in 1848 did he become the de facto leader of a political movement, of Irish nationalism. His failure then had many causes, notably the unwillingness of unarmed peasants to risk their lives and the role of priests who believed that a bloody massacre had to be prevented. But it must be acknowledged that Irish nationalism could not have had a worse leader in 1848. O’Brien failed to estimate the clamour and bluster for what it was worth, in terms of real willingness to fight. The dead hand of the reluctant general did untold damage: he failed to arm his people, proclaiming the people’s readiness to resist and discovering too late, in the field, that mere words had not forged pikes. Finally, O’Brien’s conduct of operations in Tipperary was lamentable, a byword for incompetence. Instead of striking out to gain the success that might have sent shock waves through Ireland and stimulated a genuine revolt, he spent a week moving to and fro, disappointing half-starved men who hoped to be fed and achieving nothing more inspiring than clearing out a little police station. In the final ‘battle’, if O’Brien held back from burning the house for the sake of the children, he was a decent human being, but an ineffective rebel.
O’Brien’s integrity, bravery and humanity were not enough. The situation in 1848 required qualities of judgement and ruthlessness that he did not possess, and the result was a humiliating defeat. It was complete and ignominious and he was denied the martyrdom that made Robert Emmet, author of a fiasco to rank with O’Brien’s, a venerated figure. O’Brien and his rising had no heroic aspect that could be recalled. He was consigned to the blind spot that every movement, especially a national one, must use to hide its embarrassments.
There was also much to admire, of course. O’Brien was the most noble, honourable and principled politician of his age. He was a truer nationalist than O’Connell, shunning the blandishments of Whiggery. But for 1848, he might have been remembered as a fine parliamentarian and public servant, unselfishly dedicated to the interests of his people. And, perhaps, in 1848 he was a better man, for all his many faults, than those who stood idly by.