Early in the following year he became a lieutenant-general in the Prussian service, and in command of the III Corps (with Carl von Clausewitz as his chief of staff) he took part in the Waterloo campaign. From the field of Ligny he retired with the rest of Blücher's army on Wavre, and when the other corps marched towards Waterloo, von Thielmann defended this movement against Grouchy, fighting in the Battle of Wavre (18–19 June 1815), thus contributing materially to the victory at Waterloo.