Robert Downing was 27 years old and working as a Commercial Traveller when he enlisted 3 April, 1917. he was at the time living with his widowed mother, Mary Ellen Downing, at 128 Albert Street, East Melbourne. She would later move to 49 Victoria Street, and in 1919, they were living at Glensborough, 48 Wellington Parade. 

He went into military training on 16 April at Broadmeadows Camp, and was assigned to the Machine Gun Section, No. 1 Battery, 1st Battalion Depot. From Broadmeadows, he went on to Seymour Machine Gun Depot on 21 May and was appointed Acting Corporal on 1 July. With his training completed, he was assigned to the 12 Reinforcements, 10th Machine Gun Company.

Robert Downing left for active service on 30 October, 1917, on board HMAT Aeneas A60, disembarking at Devonport, England on 27 December. He marched in for further training with the 6th Training Battalion, reverting to ranks. . He was sent to France on 1 April, marching in to the No. 1 Overflow Camp, but was then taken on strength with the 21st Battalion AIF, reverting to ranks on 31 December, 1917.

Private Dowling was again appointed as Acting Corporal on 18 January, 1918,  then headed overseas to join the fighting on 18 April, reverting to ranks once more. The war was now changing in favour of the Allied troops, as the new American forces joined in the fighting. Robert Downing was taken on strength with the 21st Battalion  on 18 April as they fought in the Somme region to oust the German forces from their positions. It was at Ville-Sur-Ancre, part of the battle of Hamel and Amiens, that he showed the courage for which he was awarded the Military Medal.

The citation read: For conspicuous gallantry and devotion to duty on the 19th May during the attack at VILLE-SUR-ANCRE. This soldier, though alone, followed some of the enemy into a cellar, and by means of great personal daring, succeeded in driving them, at the point of the bayonet,to another entrance where they were met by his Platoon Sergeant. This Sergeant was thus able to send 1 Officer and thirty Other Ranks to the rear as prisoners. Pre. Downing then used his Lewis Gun very successfully on the enemy between the Sunken Rd., known as The Caterpillar, and VILLE-SUR-ANCRE, thus accouting for many enemy casualties. His bravery and soldierly devotion to duty, to the utter disregard of self, was exceptional.

The award was mentioned in The Argus on 11 September, 1918: Mrs M.E. Downing, East Melbourne, has received a cable message from her son, Private William Hooper Downing, stating that his brother, Private Robert Clifford Downing of the 21st Battalion, has been awarded the Military Medal.

On 22 July, Robert Downing was taken ill and sent to hospital in France, returning to his battalion on 26 July. Three months later, he received the wound which incapacitated him as a machine gunner: on 5 October, he received a severe gunshot wound to the right hand, severing his forefinger. After nearly a month in hospital in France, he was sent to the Military Hospital at Exeter on 6 November, then two days later went on 2 the No. 2 Command Depot at Perham Downs. Again, The Argus reported on him: Mrs. M.E.Downing has been notified that her son, Private Robert Clifford Downing, MM, of the 21st Battalion, was admitted to War Hospital, Exeter, suffering from severe gunshot wounds in the right hand. 

Robert Downing was returned to Australia on board H T Berrima on 2 January, 1919, disembarking in Melbourne on 17 February. He was finally discharged from  the AIF on 17 July, 1919. In 1919, he was living at the 'Glensborough' 48 Wellington Parade, East Melbourne, a private hotel, asking for a copy of his discharge certificate which he needed because 'I am taking a government position (Munitions Department Finance Branch)'. However, his Electoral Roll entry for the same year shows him as living near his mother's old address during the war, at 128 Albert Street, East Melbourne with his mother and brother, William, and working as a warehouseman. He married in 1920, to Franziska Hilka Elisabeth Seehusen, but the marriage appears to have been brief. They were together in 1924, but in further Electoral Roll entries, she is not with him. In 1937, he was at 128 Albert Street, working as a hotel employee. The last two entries for him are 1943 and 1949, as a hotel employee living at the 'Glensborough'. He died that same year at Heidelberg, probably the Repatriation Hospital, aged 60.