French Revolutionary Wars
In 1792, Berthier was promoted to maréchal de camp and posted to the Army of the North. He was appointed chief of staff to Marshal Nicolas Luckner, and played a distinguished part in the Argonne campaign of Generals Dumouriez and Kellermann. He served with great credit in the War in the Vendée of 1793–1796. Berthier was made a brigade general in March 1795 and a general of division three months later.
Berthier first met Napoleon Bonaparte, when he was a general in March 1796, and was at once made chief of staff to the Army of Italy, which Bonaparte had recently been appointed to command. He served in the Italian campaign of 1796, distinguishing himself at the Battle of Lodi. In January 1797 he played an important role in the Battle of Rivoli, relieving General Joubert when the latter was attacked by the Austrian general Jozsef Alvinczi. His power of work, accuracy and quick comprehension, combined with his long and varied experience and his complete mastery of detail, made Berthier the ideal chief of staff. In this capacity, Berthier was Napoleon's most valued assistant for the rest of his career.
Berthier accompanied Napoleon throughout the campaign of 1797, and was left in charge of the army after the Treaty of Campo Formio. He was in this post in 1798 when he entered Italy, invaded the Vatican, organized the Roman Republic, and took Pope Pius VI prisoner. Berthier supervised the Pope’s relocation to Valence, where, after a tortuous journey, Pius died. The death of the Pope dealt a major blow to the Vatican's political power.
After this, Berthier joined his chief in Egypt, serving there until Napoleon's return. He assisted in the Coup of 18 Brumaire (9 November 1799), afterwards becoming Minister of War for a time. During the Battle of Marengo, Berthier was the nominal head of the Army of Reserve, but the First Consul accompanied the army and he acted in reality, as always, as chief of staff to Napoleon.
Despite serving as a staff officer, Berthier had at one point received a battlefield injury. A contemporary subordinate staff officer, Brossier, reports that at the Battle of Marengo:
The General-in-Chief Berthier gave his orders with the precision of a consummate warrior, and at Marengo maintained the reputation that he so rightly acquired in Italy and in Egypt under the orders of Bonaparte. He himself was hit by a bullet in the arm. Two of his aides-de-camp, Dutaillis and La Borde, had their horses killed.
At the close of the campaign, he was employed in civil and diplomatic business. This included a mission to Spain in August 1800, which resulted in the retrocession of Louisiana to France by the Treaty of San Ildefonso on 1 October 1800, and led to the Louisiana Purchase.
