Robertson passed out of RMC Sandhurst with honours, and joined the 1st Battalion Queen's Own Cameron Highlanders as Second Lieutenant on 22 April 1903. His regiment transferred to Dublin in 1905. He was promoted to Lieutenant effective 11 March 1909. In January 1911, he was appointed an Assistant Superintendent of Gymnasia. At the outbreak of the First World War, Robertson was recalled to the depot in Inverness, and was then briefly at Aldershot before his regiment crossed to France in September 1914 to fight on the Aisne. On 2 November 1914, Robertson was in the trenches at Ypres, when he was wounded in the arm. After having the wound dressed, he returned to his company and was wounded a second time, more seriously, and he died the following day.