Rohault de Fleury fought at the Battle of Jena in 1806. He assisted in the sieges of Stralsund and Colberg.In 1808, he was sent to Catalonia. After the defense of Barcelona, he was named battalion commander at the start of 1809. He was made an officer of the Legion of Honour in 1809 at the Third Siege of Gerona, where he led the first assault on the fort of Montjouy and was seriously wounded. He was made a lieutenant-colonel in 1814.