Aubrey Vernon Barns was the son of Joseph Steven Barns, a salesman, and his wife, Isabella Campbell Barns. At the time he enlisted on 17 October, 1915, Aubrey was loving with his parents at 45 Gipps Street, East Melbourne, and working as a civil servant. He had had 2 years training in the Senior Cadets at his school and a further nine months in the Citizens Military Forces at North Melbourne. 

 He was sent to Royal Park and attached as a Sergeant to the 21st Battalion,  before leaving forEgypt on 23 October, 1915, for Egypt on board HMAT 'Orontes'. The 21st Battalion  had been raised from rural Victoria in February,1915.  They arrived in Egypt in June 1915 and then proceeded to the Gallipoli Peninsula in late August, but the convoy was torpedoed near Lemnos, and did not arrive until 7 September, when most of the action was over. They evacuated to Egypt in December, 1915 and arrived in France in March, 1916. Aubrey Barns would not have been with them at this point, but was sent toEngland and then on to France on the 'Princess Victoria' on 3 December, 1916. New reinforcements were needed by the 21st Battalion. It had been the first battalion to commence active operations on the Western Front and had been engaged at Pozieres, Mouquet Farm and Bullecourt.  

Aubrey Barns came in at Etaples, joining the troops of the 21st on 28 December, 1916 as a temporary Corporal. In March, they took part in a major action at the first battle of Bullecourt, the disastrous first attack on the Hindenburg line, where the 4th Brigade suffered 2,339 casualties from 3,00 men, and the 4th Brigade, 950 casualties. On 1 April, 10 days before the second action at Bullecourt, Barns was promoted to temporary 2nd Lieutenant. On 19 June, he was detached and sent to the 22nd Battalion, with both battalions moving into Flanders to fight at Broodseinde in Flanders on the Ypres salient in October, 1917.

By then, Aubrey Barns was back in England. His health began to suffer by mid 1917. On 20 July, 1917, he was sent to hospital with cellulitis of the chin, caused by a streptococcal or staph infection, these days treated with antibiotics. he was admitted to the 3rd London General Hospital on 29 July, 1917, and discharged three months later, on 8 October. He was sent to Perham Downs, but on 6 December, was re-admitted to hospital with orchitis, a testicular infection, and sent to Sutton Veny Hospital. He was declared permanently unfit for active after discharge on 29 December, 1917. His appointment was terminated and he left England for Australia per HMT 'Beltana' on 2 June, 1919, arriving in Melbourne in July. He was permanently discharged on 14 march, 1920.

In 1924, he was living at 3 Harcourt Avenue, Caulfield, with his wife, Bernadette Marie, and two sisters, Alvie Capbell Barns and Isabella Campbell Barns.