Sir William Wallace Stewart Johnston, CBE, DSO, MC, ED (21 December 1887 – 21 August 1962) was a medical practitioner and an Australian Army officer who served in the First and Second World Wars.

William Wallace Stewart Johnston was born in South Yarra, Victoria, on 21 December 1887, the second son of William Edward Johnston, a barrister who later became a County Court of Victoria judge, and his wife Clara Jane, née Wallace.

Four days later he suffered gunshot wounds to the neck and chest in the Battle of Passchendaele, and was evacuated to England.

[2] He was recommended for the Victoria Cross (VC), but his citation was downgraded to the Distinguished Service Order (DSO).

While the enemy were shelling very heavily the positions where assaulting troops were assembled he went out into the open with an absolute disregard of personal safety and attended to the wounded where they lay.

He embarked for Australia on the SS Osterley on 27 September 1919, over ten months after the armistice of 11 November 1918 which ended the war, and his AIF appointment was terminated on 21 January 1920.

[11] Johnston was promoted to colonel on 13 October 1939, and commenced full-time duty as Assistant Director General of Medical Services.

He joined the Second Australian Imperial Force on 21 November 1939, with the rank of colonel, and was allocated the AIF service number VX229.

[2] On 5 February 1941, Johnston became deputy director of Medical Services (DDMS) at I Corps, which he led in the German invasion of Greece.

[12] Johnston returned to Australia in February 1942, and served as DDMS of New Guinea Force during the Kokoda Track campaign.

He became chief commissioner to the St John Ambulance Brigade in 1957, and was a member of the Australian Red Cross Society from 1945 to 1952.