Ronald Mc Millan was the elder son of Malcolm Reginald Mc Millan and his wife Jane. They lived at 230 Clarendon St., East Melbourne, and he gave this as his home address. He was only nineteen years of age and working as a clerk when he enlisted  on 17 August, 1914, virtually as soon as war had been declared. He was attached to the  6th Battalion AIF, part of the 2nd Brigade. Following training, they left got Egypt on 19 October, 1914, for Egypt on board HMAT Hororata A20.

The 6th Battalion arrivied in Egypt on 2 December, 1914. After further training, they embarked on the troop ship Galeta, to join the rest of the MEF, before leaving for the Gallipoli Peninsula. as part of the 2nd Brigage, they formed the second wave of landings at Gaba Tepe (Anzac Cove) on 25 April, then took pafrt if the failed attack on Krithia, where 133 of their men were killed in action. Malcom McMillian was not there at Krithia, having suffered a gun shot wound to his forearm on 30 April. He was transferred to a hospital ship for treatment, before being sent to England, where he was admitted to the 2nd Western General Hospital on 20 May, 1915. Following the Krithia attack, the 6th Battalion were sent back to Anzac Cove and then, in August, fought at the battle of Lone Pine. By now, they had lost 22 officers and 398 other ranks, so were returned to Egypt for reinforcements. It was here that Ronald Mc Milland rejoined the battalion, going first to the base at Serapeum on 11 March, 1916, then on the O.C. Troopship Ballarat to Alexandria. From here, they left for France.

Once in France, the 6th Battalion were deployed to the Somme  and were laced out of the front line, at Fleurbaix. Their first action was a raid on the German trenches on 12 June, followed by major action at Pozieres in July, where 102 of their number were killed.  From here they fought at Ypres, then went back to the Somme at Baizeux for winter. Malcolm McMillan was made Corporal on 4 August, 1916.

On 29 December, however, he was sick, named as  'ICT Feet', admitted first to the 3rd Ambulance Train, then on 2 January, 1917, to the 10 General Hospital at Rouen. From here, he went to the 2nd Convalescent Depot on 6 January, before being discharged to Base Depot on 11 January, and marching in from Etaples to rejoin  the 6th Battalion on 27 January. In February, the 2nd Division was at Bapaume amd in May, fought at the 2nd Battle of Bullecourt, as part of the German retreat to the Hindenburg Line. On 17 July, Malcom McMillan was made Sergeant, given the promotion in the field. He was still only 21 years of age.On 22 July, the 3rd Battle of Ypres began, at this early stage, largely an artillery battle. The battle of Pilken (31 July-2 August)and  Langemark (16-18 August) were followed by Menin Road (20-28 August), where on 21 September,  Ronald McMillan became one of 38,000 Australian casualties. He was buried at Hooge Crater Cemetery, Plot 11, Row C, Grave No ll, Passchendaele, West-Vlaanderen, Flanders, Belgium. He is remembered on the Roll of Honour Cards 145 and on Panel 47 in the Commemorative Area of the Australian War Memorial.

 An article in The Argus on 6 October, 1917 reported: 'Citizens will deeply sympathise with the City Treasurer (Mr. R. McMillan) and his wife on the death of their elder son, Lieutenant Ronald McMillan, killed in action in France. he was one of the earliest to answer the call and has seldom been away frm the firing line. He enlisted as a private and declined several offers of a commission in the Imperial Army, preferring to stick to his comrades in the AIF.'