Robertson fought and was wounded in World War I. After the war he settled in London. While working in a clothing store some of his co-workers were members of the Polytechnic Harriers, and through them he developed his love of running. In 1920, he travelled to Antwerp to cheer on his teammates from the Harriers, who were members of the British team. However, the British team was short one person and his teammates convinced their coach to let Robertson run. His inexperience showed as he finished in last place, 35 minutes behind the second to last place finisher.