Born in NSW Australia in 1891 and immigrated to New Zealand with his family in 1896. He enlisted as a gunner with No 2 Garrison Artillery Volunteers, Auckland, in 1910 and was promoted as Lieutenant at the outbreak of WW1. He then enlisted with the 3rd Auckland Mounted Rifles and sailed with the 5th Reinforcements, serving on Gallipoli until the evacuation. He then transferred to the New Zealand Field Artillery and served on the Western Front where he was promoted to the position of Major-Battery Commander. He was awarded the DSO (Distinguished Service Order) "For distinguished service in connection with military operations in France and Flanders." (London Gazette, 1 January 1919). Post-war Robert Milligan rejoined the Territorials as a Colonel and served as Aide de Camp to Lord Bledisloe. In 1939 he was appointed as Fortress Commander, Auckland, retiring from this position in 1940.

In 1935 Col. Milligan was awarded an OBE (Officer of the Most Excellent Order of the British Empire) for his services to the Territorials. He died, in Auckland, in August 1962.

For details of career see Personal Record and Cenotaph data-base.