After the Fenian Rising failed, In September 1867 O'Meagher Condon led a rescue party which attempted to save Irish Republican Brotherhood leader Thomas J. Kelly from imprisonment in Manchester, England.

During the trial, O'Meagher Condon gave a memorable speech in his own defence which ended with the rallying cry "God Save Ireland!

O'Meagher Condon was an American citizen and his sentence was commuted to life imprisonment following an intervention from the American ambassador to Britain Charles Francis Adams Sr.. O'Meagher Condon remained imprisoned until June 1878, when after semi-persistent petitioning from Irish-American politicians he was released on condition he not return to the United Kingdom for 30 years.

However, following the murder of Patrick Henry Cronin in Chicago by members of Clan na Gael which caused shock and outrage across the United States, O'Meagher Condon was forced to reduce his radicalism and thereafter withdrew from public politics, beginning a career in journalism.

[2] In 1857 O'Meagher Condon was in New York City when he encountered the Gaelic scholar and leader of the Irish nationalist organisation the Fenian Brotherhood John O'Mahony, whom he quickly befriended.

[2] In 1862, as the American Civil War began, O'Meagher Condon enlisted in the 69th New York Infantry Regiment which was composed overwhelmingly of Irish emigrants.

[2] In December 1866, the Fenian Brotherhood sent both O'Meagher Condon and Thomas J. Kelly to Ireland with the intention that they, alongside many other Irish-American veterans of the Civil War, would lead a rebellion against the British.

Instead of one unified mass rebellion that occurred all at once, the Fenian Rising was a patchwork of small uprisings across Ireland that were never able to link up and were quickly put down.

The trial was largely a political exercise - none of the defendants had been the one to have fired the fatal shot that killed Police Sergeant Brett (it had been a Dubliner by the name of Peter Rice who had actually done so).

I can only hope and pray that this prejudice will disappear —that my oppressed country will right herself some day, and that her people, so far from being looked upon with scorn and aversion, will receive what they are entitled to, the respect not only of the civilised world but of Englishmen.

I have nothing but my best wishes to send them, and my warmest feelings, and to assure them I can die as a Christian and an Irishman, and am not ashamed or afraid of anything I have done, or the consequences, before God or man.

At the eleventh hour, the American ambassador to Britain Charles Francis Adams Sr. intervened and managed to convince the British authorities to commute O'Meagher Condon's sentence to life imprisonment.

The executioner, William Calcraft, botched two of the executions and had to pull down on the legs of Larkin and O'Brien to kill them (their necks should have broken on the initial drop).

Throughout that time, his case was semi-regularly discussed in the British Parliament by figures such as John O'Connor Power (himself secretly a former Fenian and member of the Irish Republican Brotherhood) and in both houses of the United States Congress by Irish-American politicians.

[2] On 13 June 1878, this persistent petitioning paid off when both Houses of Congress passed a joint resolution asking President Rutherford B. Hayes to attempt to secure a fair trial for Condon.

The British did not concede a retrial but instead offered to release O'Meagher Condon if he promised to leave the United Kingdom and not return for at least 30 years.

[8] After the British suppressed the Land League in 1881, O'Meagher Condon responded by endorsing the Fenian Dynamite Campaign, which saw Irish Republicans travelling to England to bomb infrastructure and institutions.

[2] Following the sensational murder of Patrick Henry Cronin in Chicago and the subsequent investigation into Clan na Gael in 1889, O'Meagher Condon signed a message to the American public which denied that the organisation was guilty of ‘un-American behaviour'.

[2] On the urging of John Finerty and Patrick Egan, O'Meagher Condon became involved in the American wing of the United Irish League.