John Mackay died of his wounds recieved in France on 15 April 1918. The Week, a Brisbane-based newspaper, reported the death on 3 May stating Mackay was the third of four brothers to have enlisted and was well known in soccer circles having been selected for the Brisbane representative soccer team, an honour he received in 1913. Mackay had played for Bulimba Rangers since at least 1911 and was joined with his brothers George and William joining the club by 1915. By the end of that year all three had enlisted.
Mackay was allocated to the 31st Battalion and reached Egypt in December, and France the following June. He was promoted to Regimental Quartermaster Sergeant by the end of 1916, but in mid-1917 suffered from haematuria, or blood in his urine, which led to evacuation. He recovered by September and rejoined his unit.
On 15 April 1918 he received gunshot wounds to his thigh, foot and hand, and died three days later contrary to the newspaper report. Mackay was buried in the Querrieu Military Cemetery near Amiens.
He was engaged at the time of his death to Minnie R. Hook, of George Street Glasgow, and bequeathed a sum of £200, with anything else left to his parents, while his mother received a pension. His father wrote to the Base Records office regarding the non-delivery of Mackay’s effects, sent to him by the Battalion’s chaplain. The Records Office replied that the package had been lost at sea with the sinking of the SS Barunga.