Leaving civilian life, he enlisted in a volunteer battalion in 1792 and was wounded at the 1793 Siege of Mainz.

Under Napoleon he commanded a brigade in the IV Corps at Austerlitz in 1805, Battle of Jena in 1806 and Eylau in 1807, where he was wounded.

He became a Baron of the Empire in 1808, commanded posts in the interior and served as a military instructor.

On 16 May 1800, Levasseur was made General (Brigadier) of the 2nd brigade of the 4th Corps of the Grand Army (Commanded by Marshal Soult).

Levasseur was wounded at the Battle of Eylau in 1807 and was made a Chevalier de la Légion d'honneur.