Hartmann entered the French army in October 1804 as an infantryman in the 15th Light Infantry Regiment.

He served in the campaigns of 1814 and 1815 in the 27th Infantry Regiment, during which time he was awarded the Legion d’Honneur.

In June 1849 he was promoted to major general and given command of a brigade in the 2nd Royal Bavarian Division.

During the Austro-Prussian War Bavaria joined the Austrian side and Hartmann commanded the 4th Royal Bavarian Division in engagements against the Prussians at Rossdorf and Hettstadt.

When the Franco-Prussian War broke out, Bavaria fought on the side of its erstwhile enemy Prussia.

Hartmann lead the II Corps in the battles of Wissembourg, Wörth and Sedan.

When the German armies neared Paris he fought in engagements at Corbeil, Bourg-la-Reine, Petit-Bicètre and Moulin de la Tour.