Mortier served in the French Revolutionary Wars in the campaigns of 1792 and 1793 on the north-eastern frontier and in the Netherlands, and subsequently on the Meuse and the Rhine. Mortier was tasked by General Jacques Maurice Hatry to negotiate the surrender of the Fortress of Mainz, which he completed successfully and then returned to Paris. During the War of the Second Coalition in 1799, he was promoted to general of brigade and then general of division. During the Second Battle of Zurich, he led a force of 8,000 in the attack from Dieticon on Zurich. His conduct of the French occupation of Hanover, bringing about the Convention of Artlenburg, led Napoleon to include Mortier in the first list of marshals created in 1804.