giles was born in christchurch where he worked in a cycle shop, then as a barman at a hotel. after being initially overlooked for selection due to his times not being "up to the required standard", he represented new zealand at the 1936 summer olympics at berlin in the sprint, 1000 m time trial, and in the road race. at the 1938 british empire games in sydney he won the bronze medal in the sprint and placed ninth in the time trial.