On returning to Australia, Robertson became brigade major in the 7th Light Horse Brigade. In September 1920 he was posted to the staff of the 3rd Military District and then the 2nd Cavalry Division and the 3rd Division. In April 1922 he sat for and passed the entrance examination to the Staff College, Camberley, where his class included Majors Arthur Percival, John Smyth and Georges Vanier, and Lieutenant Colonel Harry Crerar. Robertson eventually became the first Australian to graduate with an A-grade pass.