He was chief agent at the Queensland branch of the Patriotic Assurance Company and then from 1910 was the state manager of the Insurance Office of Australia.

[2] When the First World War broke out, Cannan was appointed to command the Lytton Fixed Defences, holding this post from 5 to 31 August 1914.

He joined the Australian Imperial Force (AIF) on 23 September 1914 with the rank of lieutenant colonel, and assumed command of the 15th Battalion.

[2] The ship passed through the Suez Canal safely, arriving at Alexandria on 31 January 1915, although a Turkish force was operating in the nearby desert.

[7] In the Battle of Sari Bair on 8 August 1915, the 15th Infantry Battalion suffered heavily, having seven officers killed—including Cannan's older brother, Major D. H. Cannan—and most of the rest wounded.

[2] For "distinguished service in the field during operations in the Dardanelles", Cannan was mentioned in despatches and made a Companion of the Order of the Bath on 5 November 1915.

[11] On the night of 8 August 1916, the 15th Infantry Battalion launched an attack on the German trench in front of Mouquet Farm known as Park Lane.

However, the Suffolk Regiment on his flank was mown down by German machine gun fire and Cannan was compelled to withdraw part of his force to a more defensible position.

His clear insight into an extremely difficult tactical situation, coupled with the energy and resolution with which he directed the operations of his brigade were of the greatest value in forcing the enemy to give up his hope of holding the Hindenburg Line.

General Cannan's conduct and skill throughout the last Somme campaign gave a conspicuous example of the soldierly merit to his brigade and to the division.

The great difficulties in establishing and maintaining communications rendered the action at Bony a matter of personal leadership and in this General Cannan proved himself the right man in the right place.

[2]For his services on the Western Front, Cannan was also awarded the Belgian Croix de Guerre,[16] his citation noting his "tenacity, thoroughness and efficient organisation", "his splendid qualities of leadership", and his "personal gallantry.

[18][19][20][21][22] Cannan studied insurance practice in London under the Army Education Scheme for two months before embarking for Australia on HMAT Ancises on 22 August 1919.

Cannan was also aide de camp to the Governor General from 1 April 1920 to 21 March 1923 and honorary colonel of the 47th Infantry Battalion from 19 June 1930.

[2] On 27 May 1940, after over fifteen years on the unattached list, Cannan was appointed Inspector General of Administration at the Department of Defence Coordination.

[2] As Quartermaster General, Cannan was responsible for the Australian Army's supply, transport and engineering services throughout Australia and the South West Pacific Area.

[1] Colonel G. Drake-Brockman considered Cannan "a man of great personality and charm with tremendous drive" whose administration was "outstanding".

[25] As well as supporting the Australian Army, Cannan was also responsible for providing a broad range of goods and services to the Americans.

Nonetheless, Prime Minister John Curtin did successfully persuade General Douglas MacArthur to rationalise his use of Australian resources in order to provide accommodation for the British Pacific Fleet.

Blamey nominated him for a Knight Commander of the Order of the British Empire in September 1943, but it was refused, it not being the Labor government's policy to award knighthoods at this time.

[31] In December 1949, the government changed and Blamey wrote to the new Prime Minister, Robert Menzies, once again recommending knighthoods for a number of his generals, including Cannan.

[32] Of Cannan, it was said that his "contribution to the defence of Australia was immense; his responsibility for supply, transport and works, a giant-sized burden; his acknowledgement—nil".

He was Director of the United Nations Relief and Rehabilitation Administration in the South West Pacific from 1946 to 1947, of the Queensland division of the Australian Red Cross from 1950 to 1951, and of the Services Canteens Trust from 1948 to 1957.