Stewart started playing rugby union while he was still at school. From 1903 to 1907, he played for the first XV of the Royal Belfast Academical Institution. He played as a full back in his first year on the team, then switched to playing as a centre for the remaining years. From 1905 to 1907, he also played for Ulster in the schools' inter-provincial competition. In addition to rugby, Stewart played a number of other sports while at school. From 1904 to 1906, he played cricket with his school's first XI. He was both a good batsman and a good fielder. He was also a successful swimmer, specialising in the relay. He was part of the team who won the junior gymnastics competition in 1904, and personally won a number of prizes for sprinting.
Club level
After leaving school in 1907, Stewart joined the North of Ireland Football Club, a rugby union club based in Belfast. He played centre. In 1909, his team won the Ulster Senior League, and he was awarded the NIFC Honour Cap. He served as Vice-Captain of his club in the 1911/1912 season, and was Captain of his club in the 1913/1914 season.
Rugby international
In February 1913, Stewart was selected to play for the Ireland national rugby union team. He achieved three caps during his international career, and would have achieved more if it wasn't for the outbreak of World War I in 1914. He scored a try in his debut international match. He played in the following matches:
In September 1914, Stewart applied for a commission in the British Army. He was commissioned into the Royal Irish Rifles as a second lieutenant on 22 September 1914. He was assigned to the 10th Service Battalion, Royal Irish Rifles. He then underwent training at Newcastle, County Down. On 23 November 1914, he was made a temporarylieutenant. Next, he was posted to Ballykinlar Camp, Ballykinlar, County Down, as part of the 36th Division. In Spring 1915, he was appointed his battalion's Machine Gun Officer. In May 1915, he and the division moved to Seaford, Sussex, England. From there, they moved to Bramshott Camp, a temporary army camp on Bramshott Common, Hampshire. On 25 August 1915, he was promoted to temporary major. Stewart spent the first year of his military service, serving within the United Kingdom. On 1 October 1915, he and his battalion departed for France and the Western Front. On 18 December 1915, he was transferred to the Machine Gun Corps in the rank of temporary lieutenant with seniority from 23 November 1914. He was involved in fighting during the winter of 1915/1916. On 1 July 1916, the Battle of the Somme began. Stewart saw action and survived the deadliest day the British Army had ever seen. On 10 July 1916, he was promoted to temporary captain, and appointed officer commanding the 22nd Machine Gun Company. On 1 January 1917, he was promoted to temporary major.
Death
Stewart was killed in action on 4 October 1917 during the Battle of Broodseinde near Ypres, Belgium. He had been fighting in Glencorse Wood and was trying to seize ground from the Germans when he was killed. He was aged 28. Stewart was buried in Hooge Crater Cemetery, a Commonwealth War Graves Commission burial ground in Flanders, Belgium.
