After the war, Stewart wrote a history of the New Zealand Division, which was published in 1921 and was its main reference work for several decades.

He resumed his teaching career at Canterbury College but in 1926 returned to England, as a Professor of Latin at the University of Leeds.

In 1903, he attended the University of Edinburgh and then transferred to Trinity College, Cambridge, from which he received his Bachelor of Arts degree in 1907, majoring in Classical Studies.

He received a commission as a lieutenant and was posted to the Canterbury Battalion, New Zealand Infantry Brigade,[1] which embarked from Wellington in October 1914 for Suez, Egypt.

[4] Stewart served at Gallipoli and received a head wound during the fighting at Quinn's Post in June 1915 but, despite this, remained on the frontline.

[1] He was recommended for the Military Cross for his action at Quinn's Post and this was duly gazetted following the withdrawal of the Allies from Gallipoli.

[8] In June 1917, Stewart was awarded the Distinguished Service Order (DSO) in recognition of his leadership of his battalion during the Battle of Flers–Courcelette in September 1916.

He had planned and executed an attack by his battalion on German-held trenches and once the objective was captured, organised its defence against several counter-attacks.

[5] While on leave, on 21 February 1918, Stewart married Alexandrina Kathleen Johnston at Uttoxeter, in the county of Staffordshire in England.

He returned to New Zealand in December that year and resumed his pre-war teaching position at Canterbury College, while continuing work on his history.

[1] In a history of the University of Canterbury, published in 1973, the authors wrote that Stewart was the "most able leader and administrator ... the College [of Nottingham] ever had".

[1] A tablet in his honour was unveiled on 18 January 1935 at the premises of the Christchurch Returned Soldier's Association by the former commander of the NZEF, Alexander Godley.