Warden continued in Paris as an academician, widely recognised for his pioneering and encyclopaedic contributions to the understanding of international law, and of the geography, history and government of the Americas.

Inspired by revolutionary events in France, and despairing of the prospects for reform under the British Crown, the society resolved to secure a national and representative government by insurrection.

After repelling the first assault, the garrison of Yorkshire Fencibles withdrew, allowing the rebels to establish in the town a French revolutionary style Committee of Public Safety.

Beginning late on 12 June, Warden as "aide de camp" to Henry Munro, witnessed the rout of the main rebel conjunction at Ballynahinch.

After several weeks on a crowded prison ship, on which William Steel Dickson recalled Warden's "lively, rational and entertaining conversation", he sailed for the United States.

In a farewell address to the Presbytery, he wrote:[7]Everyone of you has both publicly and privately circulated republican morality--that religion is a personal thing--that Christ is the head of the Church--that his Kingdom is not of this world--that the will of the people should be the supreme law;--and now from terror .

[8] In the United States, Jefferson (to whom Warden continued to send political reports from Paris)[9][10] interceded with his successor in the White House, James Madison.

[8] When, at the end of 1812, Barlow unexpectedly died, Warden succeeded in having himself recognised by the French foreign minister, the duc de Bassano, as American "consul general".

[17] In 1810, Warden had not won friends in the Madison administration with his translation of the principal abolitionist reference in France, Henri Grégoire's De la Littérature Des Nègres (1808).

In his preface, Warden noted that, "ardent" in their desire to amass riches, Europeans "affected to believe, that the black colour of the negro was sufficient excuse ... to treat him worse than a brute".

But Grégoire had "proven by facts, that blacks not only possess talents, but also those nobler virtues that elevate man in the scale of being" so that for the loss of their liberty there can be no just argument or compensation.

[20]At the shrine of commerce, the ruling powers of different countries have sacrificed the most solemn principles, and individuals, by a sort of Circean enchantment, have been transformed into monsters divested of everything that constitutes the social man.

[U]nfortunately, the opinion, however ill-founded, is almost universal that every American is more or less engaged in foreign or domestic trade or barter; and the noble and independent spirit of the country is believed to be avaricious and commercial.

In 1819 his publication, in three volumes, of A Statistical, Political and Historical Account of the United States of America helped secure his election in 1826 as a corresponding member of the Académie des sciences, Morales et Politiques.

[27] In a "biographical sketch" of Warden's years in Paris published by the Institut Francais de Washington, Francis C. Haber described him as "America's cultural ambassador".

[29][30] Their terms for a competition for the best new work on "American antiquities", including maps "constructed according to exact methods" and "observations on the mores and customs of the indigenous peoples, and vocabularies of the ancient languages".

Warden does not appear to have regularly associated in Paris with Myles Byrne, William Putnam McCabe or John Allen, men who had assisted Robert Emmet in his attempt to renew the United Irish insurrection with a rising in Dublin in 1803.

Sampson was counsel for the abolitionist Manumission Society and victor in the case People v. Phillips (1813) which secured recognition in the United States for priest-penitent privilege.

Hailing him on his death in 1847 an "incarnation of a people", Honoré de Balzac noted that for twenty years O'Connell's name had filled the press of Europe as no man since Napoleon.

He was of practical assistance to the socialite when, after Napoleon's final exile in 1815, she arrived in Paris in the hope of yet finding advantage in her dissolved marriage to Jerome Bonaparte.