Stewart was commissioned into the Argyll and Sutherland Highlanders in February 1914 and on 11 August of that year became the first British soldier to land on French soil[REF] and the first to be mentioned in a despatch [REF].
As with many Army officers between the wars, Stewart was placed on half pay, but was restored to full pay as a captain on 3 June 1925[REF] On 8 September 1931, Stewart was promoted to major.