In 1835 Matthieu became involved with the Société des Fils de la Liberté (Society of the Sons of Liberty), a paramilitary organization which waged an uprising remembered to history as Papineau’s Rebellion against British rule. The youth was engaged making musket shot and cartridges and transporting arms to the scene of the fighting. The group's armed struggle was regarded as treasonous by the British government, who executed captured participants by hanging. Matthieu's participation was discovered and the youth was forced to flee Canada for refuge in the United States, crossing the border there by means of a forged passport.