Leslie William Mansell was the son of Reuben Mansell and Louisa Gowan. Born in  Ballarat East in 1894, he enlisted for World War 1 on 2o August, 1914 at the age of 20 years and eight months. He was at the time a fruit grower in Mildura, something he would return to after the war. He was 5' 1/2 " tall, with fair hair and complexion and grey eyes. By religion, he belonged to the Church of Christ. He had already had one year training in the militia, and was placed as a Gunner with the 6th Field Artillery Brigade. His embarkation record shows him as living at 30 Berry St, East Melbourne, perhaps a boarding house where he waited to be called up.

The 6th Field Artillery Brigade was formed in Melbourne on 19 October, 1914, to support the Second Infantry Division and retained its structure until January 1917. The Battery had British 18 pounder guns, thenn the standard field gun. In 1914 and 1915 the Firsat and Second Division infantry each had three Field Artillery Batteries attached. The 6th F.A.B. was attached to the 1-6th Infantry Brigades. The guns were heavy and not suited to the terrain at Gallipoli, but came into their own in France and Belgium where  field artillery was of much greater signifiance. However, it is difficult to identify where the artillery batteries fought, as they were assigned where necessity arose.

Leslie Mansell was chosen as a Gunner on 26 April, 1914 and attached to the 6th F.A.B. He served at Gallipoli, but was stricken with diarrhoea on 22 August 1915, and had to be transferred back to Alexandria on the Caledonian. On 28 February, he landed at Marseilles and was sent to the Western Front. He was in hospital again on 17 May, 1916 and was sent to the No. 18 General Hospital at Camieres. He was 65 days absent from duty, before rejoining his unit in the field on 21 September, 1916.

 On 21 September he was discharged to the A.D. Base Depot and again on 13 October, 1916,  he was first sent to one of the Casualty Clearing Station behind the lines and was transferred to hospital with gonorrhoea, he was admitted to the 1st Convalescent Depot in Boulogne, transferred to England,  rejoining the F.A.B. after 40 days of medical treatment. While in England, he was absent without leave from 29 May 1917 to 30 May.

On 30 July, 1917, he was ill again and in hospital in France. On 4 August, he was in hospital in Belgium, rejoining his unit on 11 August. On 18 August, he was in hospital again, suffering from Otorrhoea. He was sent back to England and on 30 August, 1917, was at Reading War Hospital before rejoining his unit at the front after 40 days hospital care.

On 8 March, 1918, Lesley Mansell was wounded in action, overcome by gas from a shell, and deemed to have been wounded in action. On 6 August, he was struck down with Prostatis and was moved from the No 11 Camp Hospital at Hurdcott on 6 August 1918, and sent to the 1st Australian War Hospital at Burford. He had double vesiculitis and syphilis. He was discharged to Parkhouse after 27 days and on 11 September, marched in to the No. 1 Convalescent Depot. On 18 October, he was in a camp at Devonport, England.

The military authorities decided that he was unable to return to the front, and he was returned to Australia on board the Port Hacking, leaving England on 13 December 1918 and disembarking at Melbourne on 27 January, 1919. On 28 March, 1919, Leslie Mansell was discharged from further military service.

In 1920, he married Ida Beriha Hawthorn Chambers. In 1927, he was in Geelong, living with his wife at 405 Yarra St. and working as an engineer. In He married in 1920 to later years, he returned to Mildura and took up his original work as a fruit grower. He died there in 1962, with his occupation listed as  'Retired Horticulturalist'.