In 1796, he served under Napoleon Bonaparte in the Italian campaign, and was promoted "général de division" for good service in the field. Brune commanded the French army that occupied Switzerland in 1798 and established the Helvetic Republic In the following year, he was in command of the French troops in defence of Amsterdam against the Anglo-Russian invasion of Holland under the Duke of York, in which he was completely successful – the Anglo-Russian forces were defeated in the Battle of Castricum, and compelled, after a harsh retreat, to re-embark. He rendered further good service in Vendée and in the Italian Peninsula from 1799–1801 (winning the Battle of Pozzolo).