Arrested on the eve of the 1798 rebellion, in 1802 he went into exile in France where, after being raised to the rank of General in a force that was to invade Ireland, fell out of favour with Napoleon.

Among the positions he maintained publicly in his final years were a defence of the July Revolution in Paris and opposition to what he saw as the clericalism of Daniel O'Connell's movement in Ireland.

In 1796 O'Connor joined the Society of United Irishmen, whose purpose was to overturn the Ascendancy and establish a representative national government independent both of sacramental tests and of dictation from London.

To the "free electors" of the county he commended the "entire abolition of religious distinctions" and the "establishment of a National Government", while protesting the "invasion" of the country by English and Scottish troops and the Crown's continued war against the French Republic.

[7] With Lord Edward Fitzgerald and others in the United Irish leadership in Dublin his thoughts now turned to securing French support for a republican insurrection.

In a final address "To the Irish Nation" (February 1798) he asked:Shall beggary and famine stalk through your country, so blessed with a temperate climate and a fertile soil, without the strongest suspicion that the people have not been done justice?

Shall a brave, healthy, intelligent and generous people, be doomed to the most squalid misery at home, and be famed for enterprise, activity and industry in every country but their own, without the strongest suspicion that they have been made prey to peculation, injustice, and oppression.

He assured them that “the youth of this country have totally changed their mode of thinking” regarding women and were ready to seek their “society”, their “friendship” and “alliance”.

[14] In this it was equally clear that women were being appealed to as "members of a critically-debating public":[12] While travelling to France in March 1798 he was arrested alongside Father James Coigly, a Catholic priest, and two other United Irishmen Benjamin Binns (also of the London Corresponding Society), and John Allen.

[15][3] O'Connor, able to call Charles James Fox, Lord Moira and Richard Brinsley Sheridan to testify to his character, was acquitted but was immediately re-arrested and imprisoned.

[21] According to the Nouvelle biographie générale (Paris, 1855)[22] the “openness of his character, and his unalterable attachment to the cause of liberty rendered him little agreeable to Napoleon" who, after abandoning plans for Ireland, did not again employ him.

When Britain re-opened its war with France in May 1803, Emmett sent his own emissary, Patrick Gallagher, to Paris to ask "money, arms, ammunition and officers" but not, as O'Connor had urged, for large numbers of troops.

[24] After his rising in Dublin misfired in July, and he could no longer indulge his hostility to Napoleon's imperial ambition, Emmet entrusted his plea for a French force to the rebel veteran Myles Byrne.

He supported the 1830 insurrection in Paris which overthrew the increasingly absolutist King Charles X, publishing a defence of events in the form of an open letter to General Lafayette.