Although a key supporter of the coup against the Directory that gave Napoleon supreme power, and present for his greatest victories, Berthier strongly opposed the progressive stretching of lines of communication during the Russian campaign.

Allowed to retire by the restored Bourbon regime, he died by either suicide or murder shortly before the Battle of Waterloo.

[1] He was the eldest of five surviving children of Lieutenant-Colonel Jean-Baptiste Berthier (1721–1804), an officer in the Corps of Topographical Engineers, and his first wife (married in 1746) Marie Françoise L'Huillier de La Serre.

[2] Berthier first saw action during the American Revolutionary War, in which he served from 1780 to 1783 as a staff officer under Jean-Baptiste Donatien de Vimeur, Count of Rochambeau.

[2] On his return, having attained the rank of colonel, he was employed in various staff posts and was made a Knight of Saint Louis in 1788.

[2] In July 1789, at the start of the French Revolution, Berthier was made a lieutenant-colonel as well as chief of staff of the Versailles National Guard, and in this role protected King Louis XVI's family from popular violence.

[2] He was appointed chief of staff to Marshal Nicolas Luckner, and bore a distinguished part in the Argonne campaign of Generals Dumouriez and Kellermann.

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.

He was in this post in 1798 when he entered Italy, invaded the Vatican, organized the Roman Republic, and took Pope Pius VI prisoner.

He served in Germany in 1813, and France in 1814, fulfilling, until the fall of the French Empire, the functions of chief of staff of the Grande Armée.

[6] The manner of his death remains uncertain because he fell from a casement window with a sill 4 ft (1.2 m) from the floor, making an accident seem unlikely.

[7] According to some accounts, he was assassinated by members of a secret society, while others say he threw himself from the window, maddened at the sight of Russian troops marching to invade France.

Despite the fact that his merit as a general was completely overshadowed by the genius of Napoleon, Berthier was nevertheless renowned for his excellent organising skills and being able to understand and carry out the emperor's directions to the minutest detail.

[8]In 1796, Berthier fell in love with Giuseppa Carcano, marquise Visconti di Borgorato, who was to be his mistress for the duration of the First French Empire, despite the emperor's disapproval.

Even when Napoleon forced him to marry a Bavarian princess, the Duchess Maria Elisabeth, in 1808, Berthier managed to keep his mistress and his wife together under the same roof, a state of affairs which infuriated the emperor.

[9] On 9 March 1808, Berthier married Elisabeth who was the only daughter of Duke Wilhelm in Bavaria and Countess Palatine Maria Anna of Zweibrücken-Birkenfeld-Rappoltstein,[10] the sister of King Maximilian I Joseph of Bavaria, and a relative of the Russian emperor through the Wittelsbach line on the Bavarian side and Prussian (Mecklenburg) side of her lineage.