During the Second World War, Hakewill-Smith served as Commanding Officer (CO) of the 5th Battalion, Devonshire Regiment, for several months from May 1940 and, from September that year, as the CO of the 4th/5th Battalion, Royal Scots Fusiliers, as an acting lieutenant colonel. He was promoted to temporary brigadier on 30 March 1941, and commanded the 157th Infantry Brigade until late March 1942. He then became Director of Organization at the War Office, before assuming command of the 155th Infantry Brigade in mid-February 1943. On 26 December, promoted to temporary major general, he assumed command of the mountain warfare-trained 52nd (Lowland) Infantry Division from Major General Neil Ritchie as its General Officer Commanding. He commanded the 52nd Division during the campaign in North-West Europe from October 1944 until May 1945.