John Guise Cowley was born in Mussoorie, India, 20 August 1905, the son of Henry Guise Beatson Cowley and Ethel Florence Prowse. He was brought up in Dorset and educated at Wellington College and the Royal Military Academy, Woolwich. He married Irene Sybil Millen in 1947, with whom he had one son and three daughters.

He was commissioned in the Royal Engineers, 1925, posted to Aldershot, and promoted Lieutenant, 1927. He served with the Madras Sappers and Miners at Bangalore and Quetta, 1932-6, and, in the latter place, helped rescue patients from the ruined hospital during the earthquake of 1935. He was promoted Captain, 1936. He was an instructor at the Royal Military Academy, Woolwich, 1936-9, and a student at the Staff College, Camberley, 1939.

On the outbreak of the Second World War, he was sent to the War Office, where he organised the dispatch of the Cavalry Division to Palestine. He went to the Western Desert, 1940, and was beseiged in Tobruk, 1941. After being evacuated from Tobruk, he was put in charge of the docks at Alexandria, 1941. He was appointed to the staff of 7 Armoured Division and then 30 Corps, 1941-2. He was promoted Major, 1940, Lieutenant-Colonel, 1941, and Brigadier, 1943. He was on the British Army Staff, Washington, 1942-3, and an instructor at the US Command and Staff School, Fort Leavenworth, Kansas, 1942-3. He was posted to Allied Forces HQ in Algeria and later Caserta, in Italy, 1943-4. He joined the staff of 21 Army Group in Brussels to help refugees and the homeless in Belgium and Holland, 1944. At the end of the war, he moved to Minden in the British sector of Germany.

He was a student at the Imperial Defence College; on the Defence Research Policy staff; and Director of Administrative Planning at the War Office. He was Chief-of-Staff, Eastern Command, 1953-6; Vice-Quatermaster General at the War Office, 1956-7; and Controller of Munitions at the Ministry of Supply, 1957-60. He was promoted Major-General, 1953, and Lieutenant-General, 1957. Finally, he was Master-General of the Ordnance at the War Office, 1960-2. He retired from the Army in 1962.

He retired to the New Forest, Hampshire, and died on 7 January 1993.

He was awarded the Albert Medal (the civilian Victoria Cross) for the bravery of his actions during the Quetta earthquake. In 1971, his Albert Medal was converted to the George Cross. He was also appointed OBE, 1943; CBE, 1946; CB, 1954; and KBE, 1958.