Gerlach attended the Joachimsthal Gymnasium in Berlin and in 1803 was commissioned as a corporal in the infantry regiment "von Arnim" in the Prussian Army.

After King Frederick William III’s proclamation An Mein Volk (‘To my People’) which appealed for support against Napoleon, Gerlach was reactivated in the army as a second lieutenant and assigned to General Blücher's staff.

During the Wars of Liberation he took part in the battles at Großgörschen, Bautzen, Katzbach, Leipzig, La Rothière, Paris, Ligny and Wavre.

Leopold von Gerlach died in 1861 as a result of a cold he contracted at the funeral of Frederick William IV.

A large part of Leopold von Gerlach's estate, which was kept in the Stettin State Archives, was lost in 1945 during World War II.