When war broke out again in 1815 after Napoleon's escape from Elba, Hardinge returned to active service as a brigadier. Attached to the staff of the allied Prussian Army under Marshal Blucher, he was present at the Battle of Ligny on 16 June 1815, where he lost his left hand by a shot, and thus was not present at Waterloo two days later. Wellington presented him with a sword that had belonged to Napoleon. Hardinge remained attached to the Prussian army of occupation in France until 1818.