When World War I commenced in 1914, MacDonald attempted to enlist in the Australian Army but claimed he was rejected due to having bad teeth. However, there is no Attestation Paper for this enlistment in the National Archives of Australia. It is possible the Attestation Paper has been misplaced as the Archives acknowledge that records, although comprehensive, are not complete. After his rejection, he travelled to
Queensland to work in the
canefields. MacDonald fought in the
First Battle of Passchendaele, walking 96 kilometres over three days to reach
Ypres. When the Germans attacked, MacDonald showed bravery and courage by working in a vulnerable position in an area that was continually under fire, determined to keep communication lines open between the battalion's forward position and headquarters. The battalion suffered a loss of 248 men who were killed during the attack. MacDonald later recalled that on one occasion he was tying a knot in a communication cable when eight shells exploded nearby causing the putty in his pocket to burn into his leg. A friend who had seen the incident reported MacDonald as dead, which was later corrected when MacDonald returned to base alive. When
World War II commenced, MacDonald was keen to travel overseas to once again fight for his country, and therefore re-enlisted in the army. However, after the army decided he was too old to see action, MacDonald was relegated to the
Victoria Barracks in
Sydney where he served five years undertaking clerical work and providing administrative support during World War II. ==Honours==