George Keppel had been previously in his military life commissioned an ensign in the Coldstream Guards in 1738, becoming a captain-lieutenant of the 1st Regiment of Dragoons in 1741, aged 17, and a captain-lieutenant of the Coldstreams on 7 April 1743. Appointed aide-de-camp to the Duke of Cumberland in February 1745, was promoted to captain and lieutenant-colonel on 27 May 1745. The next year, he was promoted colonel and made aide-de-camp to the King on 24 April 1746. He had fought at the Battle of Culloden with his father and carried the dispatch of Cumberland's success to London.