As a Colonel in the 1st Regiment of Life Guards Sir John was appointed Deputy Adjutant-General of Cavalry at the start the Waterloo Campaign. He led the charge of the Life Guards during the holding action at Genappe on the 17th during the Anglo-allied retreat from Quatre Bras to Waterloo. He was severely wounded during the subsequent battle. Sir Walter Scott, in "Paul's Letters to his Kinsfolk", described his feats at the attack on the escarpment of Mont-Saint-Jean, a ridge to the south of the village of Waterloo: