Educated at the Royal Military College, Sandhurst, Cox joined the British Army and was commissioned as a second lieutenant in the King's Shropshire Light Infantry on 29 January 1925.

[1][2] After attending the Staff College, Camberley, he served in World War II, initially as a staff officer and then as Commanding Officer (CO) of the 11th Battalion, Worcestershire Regiment from July 1942 (reconstituted as the 1st Battalion, Worcestershire Regiment from January 1943) until September 1943.

[3] After the war he became brigadier on the general staff at Western Command in 1948, deputy director of Infantry in June 1953 and Chief of Staff at Southern Command in March 1954.

[2] He went on to be General Officer Commanding (GOC) Mid West District and 53rd (Welsh) Infantry Division in March 1955 and Director, Territorial Army, Cadets and Home Guard in February 1958.

[2] Cox became colonel of the King's Shropshire Light Infantry in November 1957.