William entered the Royal Military Academy Sandhurst, completing a 44-week course as an Officer Cadet and being commissioned as a British Army officer.

William joined the Household Cavalry (Blues and Royals) as a second lieutenant, commanding a troop of four Scimitar armoured reconnaissance vehicles.

William undertook attachments to the Royal Air Force and the Royal Navy, gaining experience in all three major branches of the armed services.

William trained as a search and rescue pilot with the RAF Search and Rescue Force, conducting 156 operations and qualifying as an operational captain.

William served as an air ambulance pilot with the East Anglian Air Ambulance, further developing his flying skills.