He was born at Pont-à-Mousson in Meurthe and was a student at the École Polytechnique before joining the 1st Artillery Regiment in Napoleon’s army in Germany in 1804. He participated in the 1805 Ulm Campaign, and was wounded in the battle of Dürenstein. In 1807, he was part of the French military mission to the Ottoman Sultan Selim III, tasked with shoring up the defences of Constantinople. Fabvier then managed to join the diplomatic mission of General Charles Mathieu Gardanne, Napoleon's envoy to Persia, who tried to combat British and Russian influence in the region. Fabvier was tasked with creating an artillery school and arsenal at Esfahān, and was awarded the newly constituted Order of the Lion and the Sun for his efforts.