Powles was the son of Colonel Charles Guy Powles, a decorated military soldier who served with distinction during World War I as brigade major of New Zealand Mounted Rifles Brigade 1914–1916 and AA & QMG ANZAC Mounted Division 1916–1918.
During the war, Powles went on active military service, and achieved the rank of colonel, commanding the New Zealand artillery regiment in the South Pacific at Guadalcanal and New Caledonia.
Powles was a founding member of the New Zealand Institute of International Affairs in 1934, along with Alister McIntosh, John Cawte Beaglehole, and William Sutch.
Powles joined the fledgling Department of External Affairs in 1945, working alongside such notable figures as Alister McIntosh, George Laking, and later Frank Corner and Merwyn Norrish.
Powles was appointed a Knight Commander of the Order of the British Empire in the 1961 New Year Honours, and was made New Zealand's first Ombudsman in 1962.