Knowland was born on 16 August 1922 in Catford, Kent and attended Elmwood Primary School in Croydon. He joined the British Army, the Royal Norfolk Regiment, in 1940 as a private and was commissioned before the end of the next year.

On 31 January 1945 near Kangaw, Burma, Lieutenant Knowland was in command of a forward platoon of a troop which was being heavily attacked – some 300 of the enemy concentrating on his 24 men. During the attacks he moved among the men distributing ammunition and contributing with rifle fire and throwing grenades at the enemy. When the crew of one of his forward Bren light machine guns had been wounded, he rushed forward to man it himself. The enemy was only 10 yards (9.1 m) away but below the level of the trench so to fire into them he stood up. He continued to fire until the casualties had been evacuated. A replacement gun team that had been sent for were injured while moving up and he stayed with the gun until a third team arrived.