William Dunstan was born on 5 June 1920 to William and Marjorie Lillian Stewart Dunstan at Prahran Victoria. His father had served in the First World War with the 7th Battalion fighting at the battle of Lone Pine. His action during this battled earned him a Victoria Cross.
William Dunstan enlisted at the age of 19 in the 2nd Australian Imperial Force on 7 May 1940 as a gunner at Caulfield, Victoria. He was assigned to the 2/4th Field Regiment and trained at Puckapunyal until the unit was deployed to the Middle East in October 1940. Dunstan fought with this unit as part of the Syrian Campaign from June to July 1941. It was during 1941 that Dunstan was promoted to a sergeant.
In May 1942 after the unit had returned to Australia, Dunstan, along with the other non–commissioned officers in his unit, were made a lieutenants and transferred to 16th Field Regiment, a militia unit in the first Australian Armoured Division. He trained with this unit in Northern New South Wales and Western Australia, but it was made clear to Dunstan that this division was unlikely to ever leave Australia. Unhappy with this prospect, Dunstan applied to join the British Army in the Middle East. His request was granted. He was sent to Egypt and was discharged from the 2nd Australian Imperial Force on 13 January 1944. Dunstan was required to undertake further training in Egypt before being assigned to the 91st Field Regiment in Anzio, Italy, taking part in the Battle of Anzio.
Dunstan, along with the rest of the 5th Division, was taken out of action in July 1944 and sent to Palestine to rest and re-equip. During this time he was promoted to captain and trained in Palestine, Lebanon and Syria- many of the places he had seen while serving with the 2/4th Field Regiment. The unit was then called into Europe to fight in the final stages of the war, being part of the British 21st Army Group to cross the Elbe River in April 1945. After VE day in May 1945, his unit was part of the occupation forces in Germany.
Hoping to get closer to Australia, Dunstan volunteered for services in the Far East. He was transferred to 178th Assault Field Regiment under South East Asian Command based in Batavia, Indonesia in December 1945. Here he was battery captain of the 122 Battery, which was engaged in the Indonesian War of Independence. In May of 1946 he was sent back to Australia for discharge and formally left the British Army in early July 1946.

Dunstan married Patricia Marjorie Blew on the 24 December 1952 and they had two children.
William Dunstan died on the 23 October 2015 at New South Wales.