Leslie Cooper was a hairdresser, possibly working at Thellier Hairdresser, Prahran, where he had done his apprenticeship. He was a month off his 29th birthday when he enlisted on 12 February, 1916, and at 6' 1" tall, must have seemed liked an ideal recruit. He gave as his next of kin his father, William Cooper, who lived at Hethersett Grove, Murrumbeena.

Leslie Cooper was attached to the newly formed 37th Battalion, established at Seymour in February 1916 and drawing recruits from the Seymour area, North-Eastern Victoria and Melbourne. Afer training at Broadmeadows,they embarked for the Western Front on 3 June, 1916, on HMAT Persic A34, landing at Plymouth on 25 July to undertake more training in Britain. On 22 November, the new recruits left for France from Southampton to go to the Front. Within a week after landing on 23 November, they were in the trenches in the biotter winter of 1916-17 and mainly engaged in raiding German trenches. Leslie Cooper was sent to hospital on 9 January, 1917, suffering from varicose veins. His condition must have been bad: he was let out from hospital back to the front, but almost immediately readmitted on 13 January. This seems to have marked  the end of his active role in the war. He was taken off strength of the 37th Battalion, with the day of his last payment 21 March, 1917, and transferred to the 38th, where he served at Headquarters (AGBD) in France. 

Leslie Cooper left France for England on 28 February, 1919, and on 12 May, was returned to Australia on the Soudan. There is little else in his record, save letters to the Department from his sister and a note that he died in 1968. However, the Death index does not have a record of his death and, given that he had no second name and no post war address, it is difficult to find other information.