When World War I began, Coles enlisted as a private, fighting at Gallipoli and on the Western Front in France, and was wounded on three occasions before being commissioned as a lieutenant.

He joined with two brothers and an uncle to open a variety store in Collingwood, a working-class suburb of Melbourne.

Coles was one of the two independent parliamentarians (the other was Alexander Wilson) who held the balance of power through the early years of the Second World War.

[1] After Menzies was deposed, both Coles and Wilson men crossed the floor in 1941 to remove the hapless UAP-Country Party government of Arthur Fadden.

Governor-General Lord Gowrie was reluctant to call an election for a Parliament barely a year old, especially given the international situation.

He summoned Coles and Wilson and made them promise that if he named Labor leader John Curtin prime minister, they would support him for the remainder of the Parliament to end the instability in government.