Rex Hewer was educated at Bloxham School, where he was a member of the Officer Training Corps. He commissioned into the Royal Field Artillery on 12 October 1914, and saw active service in the First World War. He was awarded the Military Cross on 17 December 1917.
Following the war, he served with the 7th Dragoon Guards, and later with the 7th Queen’s Own Hussars. Between the wars he held command positions in the Royal Armoured Corps.
At the start of the Second World War, Hewer was serving as Deputy Assistant Quartermaster-General, War Office.
Between 1939 and 1940 he fought in the Battle of France as Assistant Quartermaster-General of Movements with the British Expeditionary Force.
Following the fall of France, he became Assistant Adjutant & Quartermaster-General, Middle East Command, and was later Director of Movements with the same formation. He was Mentioned in Dispatches for services in the Middle East on 30 December 1941.
He was promoted to Colonel on 27 June 1942.
He was invested as an Officer of the Order of the British Empire in July 1940 and made a Commander of the same order on 9 September 1942 and was made Acting Major-General on 28 March 1943.
He was further mentioned in dispatches on 6 April 1944 for distinguished service in the Middle East.
Between 1945 and 1947 he was Deputy Director-General of the European Central Inland Transport Organisation.
He retired on 29 May 1948 and was granted the honorary rank of Major-General.