Irving Russell Flett was born at Albert Park, Victoria on 23 September 1887. A salesman, Flett lived in Brighton, Victoria with his parents and a brother, Walter. Flett was appointed as second lieutenant in the newly raised 23rd Battalion on 24 March 1915. Flett departed Melbourne aboard HMAT Euripides on 10 May 1915. He was promoted to the rank of lieutenant on 26 August 1915, just before the 23rd Battalion landed at Gallipoli on 4 September 1915. The battalion were soon manning the difficult and dangerous trenches at Lone Pine which they occupied alternately with the 24th Battalion, until the evacuation in December 1915.

Following the evacuation, Flett was sent, via Egypt, to France with the 23rd Battalion. The battalion experienced a relatively gentle introduction to the Western Front via the Armentières sector in northern France in April 1916. However, the battalion was to experience substantial casualties during the horrific battles of Pozières and Mouquet Farm in July. Flett was amongst these casualties and was killed in action on 28 July 1916 at Pozières, France, aged 29. Irving Flett was buried on the battlefield near the ruins of Pozières and is commemorated on the Villers-Bretonneux Memorial, France.