William Gordon Farquhar was born in Woongarra, Bundaberg, Queensland in 1889 to William Gordon and Margaret Wallace Farquhar. Prior to enlisting, he spent six years as a senior cadet and worked as a surveyor. Farquhar enlisted in Brisbane, Queensland on 18 August 1914 as a Sapper and was assigned to the 3rd Field Company Engineers where he was soon promoted to lance corporal. He embarked for Egypt on 22 September 1914 aboard HMAT Geelong. After training in Egypt, Farquhar served at Gallipoli with 3rd Field Company Engineers. He was promoted to sergeant on 15 May 1915. He was transferred in July 1915 to the 8th Field Company Engineers (at that time 5th Field Company Engineers) in Egypt.

Farquhar was commissioned as a second Lieutenant on 26 July 1915. Farquhar retuned to Gallipoli on 12 September, leading No. 3 Section at Quinn's Post, until the evacuation in December. Farquhar was promoted to lieutenant during this time. Between January and June 1916, the 8th Field Company Engineers trained in Egypt where Farquhar was promoted to captain on 14 March. The unit embarked for France in June 1916. Farquhar was promoted to major on 21 March 1917 and took command of the 8th Field Company Engineers from 23 March 1917. He was twice Mentioned in Despatches (December 1917 and December 1918) and was awarded the Distinguished Service Order on 1 January 1918 for his actions on the Somme and at Lagnicourt. He was awarded the Croix de Guerre (Belgian) on 5 April 1919 "for continued gallant and devoted services under fire". Farquhar returned to Australia in February 1919 aboard HMAT Berrima.