William Downie was born in Kensington Victoria, but at the time of his enlistment was at 57 Angus St., Jolimont, Victoria. He was a married man, 27 years old, with fair hair and blue eyes, Presbyterian by religion, and working as a salesman. He enlisted early and was placed in D Section of the 4th Field Ambulance. He must have impressed his trainers, because on completion he was appointed as Staff Sergeant. 

He enlisted on 12 September, 1914, and on 16 November was  appointed as Staff Sergeant (Dispenser). His record does not say on which ship he travelled, bu he was there at Anzac Cove, Gallipoli. and served through that campaign. On 13 May, 1915, he was sent to hospital to have his teeth seen to, though whether this was as a result of war or just tooth decay is not noted in his record.  On 27 August, 1915, he was in hospital with influenza, probably in Egypt. On 5 March, 1916, he embarked on the Caledonia from Alexandria and disembarked at Marseilles, where, on 12 March,  he was taken on strength with the 14th Field Ambulance.

He had another bout of influenza in August, spending three weeks in the General Hospital ,Wandsworth, before returning to France. William Downie served at the Western  Front until July 1917, when he wrote a letter to ask that he be dismissed from service and returned to Australia:

My wife has been a constant sufferer for two years and has been under two consuption (sic) specialists for this period. she was ordered away from Victoria to Queensland which meant parting with all relations and friends ...  I feel, sir, that I should be with her and for this reason, make this urgent appeal ... I feel sure I have done my duty to my country in the past and will always remember my obligation to it in future.

The army authorities agreed to his release from service. He was returned from France on 2 September, 1917, with and given leave to report to Southall for temporary duty on 3 September for nursing duties with the 2nd Australian General Hospital. On 24 September he was detached from duty with the A. G. H. and transferred to AIF Headquarters, London.

On 22 December, 1917, he embarked for Australia. He corresponded with Base Records on 23 April, 1928, when he asked that his medals be forwarded to him and on 1932 was living at 29 Argyle St, Kew, Victoria.