He spent his early childhood in the United States and was sent to England in the 1890s to be educated at Eastfield House, Ditchling, Sussex, and at Malvern College.

[5] Between 1913 and 1914, he gained experience in the offices of architects in London, Boston, and New York City, and worked on a project at Le Touquet in northern France.

[2] Robertson joined the British Army during the First World War and served in France from 1915 to 1919, rising to the rank of colonel.

He was awarded the British Military Cross, the French Légion d'honneur and Black Star, and the American Certificate of Merit Medal.

[2] With Le Corbusier, Oscar Niemeyer, Sven Markelius, and others, Robertson was a member of the Board of Design Consultants which assisted Wallace Harrison with the design of the United Nations Headquarters in New York City, built between 1947 and 1952 in reinforced concrete and aluminium, with glass curtain walls.

[2] His Schloss Freudenberg, at Rotkreuz in Switzerland, is a country house built for Erwin Hürlimann, chairman of Swiss Reinsurance, between 1929 and 1933.