Following his coronation as Emperor of the French in 1804, Napoleon made Brune a Marshal of the Empire ("Maréchal d'Empire") while he was still in Constantinople. During the campaigns against Austria during the War of the Third Coalition, Marshal Brune commanded the army in Boulogne from 1805 to 1807 overseeing drilling and keeping a watchful eye on the British. In 1807 Brune was appointed Governor General for the Hanseatic Ports and in 1808, Brune held a command of troops fighting in War of the Fourth Coalition and occupied Swedish Pomerania, taking Stralsund and the Island of Rugen. Despite these victories, his staunch republicanism and a meeting with Gustav IV Adolf of Sweden raised Napoleon's suspicions only made worse by Brune who refused to talk to Napoleon about it claiming simply that "It's a lie". Brune made his biggest blunder while drafting a treaty between France and Sweden when he wrote "the French army" instead of "His Imperial Majesty's Army". Whether an intentional insult or act of incompetence, Napoleon was infuriated and Brune was removed from duty. He then spent the next years at his country estate in disgrace and was not re-employed until 1815.