Under the Empire he was the third and last Grand marshal of the palace, the head of the Military Household of emperor Napoleon Bonaparte, whom he followed in both the exiles to Elba and Saint-Helena.

In 1811, the Emperor appointed Bertrand governor of the Illyrian Provinces and during the German campaign of 1813, he commanded IV Corps which he led in the battles of Großbeeren, Dennewitz, Wartenburg and Leipzig.

In 1840 he was chosen to accompany the Prince of Joinville to St. Helena to retrieve and bring Napoleon's remains to France, in what became known as the retour des cendres.

[2] During his exile on St Helena he compiled Napoléon's confidences in a book entitled "Les cahiers de Sainte Hélène".

According to historians, this document is more accurate than Las Cases' "Memorial de Sainte Hélène" which reached a much larger amount of readers in the 19 century as it was designed for propangadistic purposes.