Jock Stewart first attracted attention as a future champion in 1911, when he finished fourth in the NCU 50-mile Championship at Birmingham. The first three men home were crack riders Clarrie Kingsbury, Charles Denny and Henry Lee but, despite their presence, Stewart led at 10-, 20- and 30-miles, and was second at 40-miles. The runner-up in the 1913 Southern Counties 50-mile Championship at Herne Hill, Stewart’s cycling career was put on hold during World War I. However, after the hostilities, he won the 1919 Southern Counties 50-mile tandem-paced title, for the third time, and therefore made the “Cycling Trophy” his permanent property. That same year, Stewart was third in the NCU 1-mile Championship behind future fellow Olympians Harry Ryan and William Ormston. In 1920, Stewart and Ryan won the Madison event at Herne Hill, and the following year were beaten on the line trying to retain their title.
A Metropolitan Police officer, Stewart was promoted to inspector in 1924, and stationed at Kensington High Street. He competed in many police sports events, and proved himself as an all-rounder and, as well as winning many cycling events, was a good track and field athlete and won events ranging from sprint, to middle-distance, and he was even a useful shot putter. He was described by Athletic News in 1924 as the “Genial and hefty Kentish Wheeler”. When Jack Holdsworth broke his own 24-hour tandem-paced record at Herne Hill in 1929, Stewart was one of his pacers.