Thelwall's career as an editor and journalist was quite successful, but the highlight of this period was his political activism. In the wake of the French Revolution, he became "intoxicated in the French doctrines of the day".Quoted in Seccombe, T. John Thelwall, in Stephen L. and Lee S. (eds.), Dictionary of National Biography, Smith Elder & Co., London 1885–1900. He started to hold talks in London's radical societies and, having made acquaintance with fellow radical John Horne Tooke, and in 1792 co-founded the federation of radical clubs and societies, the London Corresponding Society.
