William Dunstan, a clerk from Ballarat East, Victoria, enlisted in the 7th Battalion, 6th Reinforcements from Melbourne on 3 June 1915. His unit embarked from Melbourne, Victoria, on board HMAT A62 Wandilla on 17 June 1915. From 5 August he was an acting corporal with the 7th on Gallipoli where four days later he won the Victoria Cross for conspicuous bravery at Lone Pine.

Early on 9 August the Turks made a determined counter-attack on a newly captured trench held by Lieutenant Frederick Tubb and ten men. Two men were told to remain on the floor of the trench to catch and throw back enemy bombs or to smother their explosions with overcoats; both were soon mutilated. Tubb, with Corporal Dunstan, Corporal Alexander Burton and six others, kept firing over the parapet. Several bombs burst simultaneously in the trench killing or wounding five men. Tubb continued to fight, supported only by Dunstan and Burton until a violent explosion blew down the barricade. Tubb drove the Turks off and Dunstan and Burton were rebuilding it when a bomb burst between them, killing Burton and temporarily blinding Dunstan.

Commenced return to Australia from Suez on board HT 'Ulysses', 3 September 1915; disembarked Melbourne, 30 September 1915; discharged, 1 February 1916.

His brother, Alfred David Dunstan (Tree No 3457) also served.
Tree No. 713