When Prussia entered the Sixth Coalition in 1813, Grolman served as a Major and commanded a Brandenburg Landwehr battalion. He participated in the Battle of Hagelberg and the blockades of Magdeburg and Wesel. In July 1814 Grolman returned to his magistracy, but took command of his Landwehr battalion the following year during the Hundred Days. For his leadership at Fleurus and Wavre he was awarded the Iron Cross 1st Class.