Tharreau enthusiastically adopted the revolutionary cause and joined the Maine-et-Loire volunteers in 1792. He quickly rose through the command ranks. By 1795, he was chief of staff of the Army of the Ardennes. He helped to defend Zurich in the French army's defeat at the First Battle of Zurich in 1799, and participated in the French victory over the combined Austrian and Russian forces later that summer. After the successes of the 1809 campaign on the Danube, he was part of the jubilant force entering the Habsburg capital of Vienna.