Garnet entered the Royal Military College of Canada in Kingston, Ontario, taking the top entrance examination score. While there, he rose to battalion sergeant-major, and was awarded the gold medal, and the sword of honour. Upon graduation in 1901, he was placed on the Reserve of Officers as a Lieutenant of Engineers, and was offered a commission with the Royal Engineers at Woolwich, England. However, his father opposed this, so for some time he worked as an engineer for the Canadian Northern Railway, and later became Chief Engineer for the Dominion Department of Public Works on Vancouver Island. On arriving in Victoria, British Columbia, Hughes joined the Canadian militia as a part-time officer. He also met Elizabeth Irene Bayliss Newling and married her in 1910. The couple had one son, Samuel.