He joined the Scots Guards as a subaltern in 1939, and in June 1940 volunteered for the new No.8 Commando under Lt. Col. Robert Laycock which became part of Force Z then Layforce. After Layforce (and No.8 Commando) were disbanded on 1st August 1941, Stirling convinced the Army high command to allow him to form a new Special Forces unit which was given the deliberately misleadingly name "L Detachment, Special Air Service Brigade" to enforce an existing deception of a parachute brigade existing in North Africa. He was later captured by the Italians and spent the rest of the war at Colditz prisoner of war camp.
He was knighted in 1990, and died later that year.