Leslie George Fussell was born at Ballarat on 3 November 1883. He was married to Ruby Evelyn Fussell and was employed as a bank clerk, when he was commissioned into the Australian Imperial Force as a lieutenant on 7 May 1915. He departed Australia with the 17th Battalion aboard HMAT Themistocles only five days later.

The 17th Battalion trained in Egypt before landing at Anzac Cove on 20 August 1915. At Gallipoli, the Battalion participated in the last action of the August Offensive and then spent the remainder of its time defending Quinn's Post. After the evacuation, Fussell proceeded to France with the 17th Battalion and by June 1916 had become a captain. He fought at Pozières between 25 July and 5 August 1916 and in Belgium until the end of the year.

Fussell spent most of 1917 away from the 17th Battalion as between 3 January and 23 July 1917, he was seconded for duty to the Ist Anzac Corps School. He was awarded the Military Cross on 5 June 1917 for his consistent devotion to duty, and was promoted to major on 22 June 1917. After a short period back with the 17th Battalion, hewas attached to the 2nd Australian Division as a brigade major trainee from 13 August 1917. He returned to his unit on 23 November 1917 and remained with the 17th Battalion through most of 1918.

The 17th Battalion helped to thwart the German Spring Offensive of 1918 after which the Allied armies turned to the offensive. During this period, the 17th Battalion participated in a number of battles: Amiens on 8 August, the attack on Mont St Quentin on 31 August, and the forcing of the Beaurevoir Line around Montbrehain on 3 October. Montbrehain was the battalion's last battle as it was in training when the armistice was declared. Active throughout 1919 with demobilisation of the AIF, Leslie Fussell returned to Australia in early 1920 and his military appointment was terminated on 16 June 1920.