Stewart was born Harold James Valentine Stewart on 12 February 1898. He was the fourth child of James and Matilda Stewart of Collingwood.
Stewart volunteered for service with the Australian Imperial Force with the consent of his father at Melbourne on 27 June 1915. He listed his age as simply "18 years" as he would have only turned 17 less than five months prior to enlisting.
Pte Stewart was assigned to the 2nd Reinforcements of the 24th Australian Infantry Battalion and embarked from Melbourne aboard HMAT Demosthenes on 15 July 1915.
On 14 October 1917, the Brigadier-General, Commanding Second Australian Division recommended Pte Stewart for the Military Medal:
For conspicuous gallantry in the advance on BROODSEINDE RIDGE on 4th Oct. Whilst his platoon was ?????, heavy enemy shell fire at the JOT a Lewis Gunner was hit. Pte STEWART picked up the panniers and advanced with the platoon. A little later No 1 of the Gun was hit, so STEWART took up the gun and tool bags carrying them through with the panniers to the Blue Line. Here he employed the gun with marked success in inflicting casualties on the enemy. In addition to the above STEWART did yeoman work in aiding the relieving Company. His coolness and initiative aided much good work being done in the consolidation.
The citation for Pte Stewart's Military Medal appeared in the London Gazette on 14 January 1918, and the Commonwealth of Australia Gazette on 23 May.
On 21 October the Temporary Commander of the 6th Australian Infantry Brigade, LTCOL Wiltshire, recommended Pte Stewart for a bar to his Military Medal:
During the operations at MONTBREHAIN, East of PERONNE, on Oct 5th 1918, this man was a Company Runner, and at one stage found his Company was held up by an enemy Machine Gune post.
Acting on his own initiative STEWART rushed the post single-handed, shot two of the crew and forced the remainder to surrender.
Throughout the day he exhibited splendid courage in carrying frequent messages from the line to Coy and Bn Hdqrs, and late in the afternoon was so exhausted that he was evacuated to the Transport Lines by the Medical Officer.
The citation for Pte Stewart's Military Medal Bar did not appear in the London Gazette until 23 July 1919.
Stewart married Jean Lorraine Kelton in Albury in 1924. He died on 21 October 1956 at age 58 and is now buried with his wife (who died 29 July 1978) at the Waugh Road Monumental Cemetery, North Albury.