Garrett was born in Kew, in Melbourne, Victoria. He was educated at Workingman's College (now RMIT University) and the University of Melbourne. At the age of 26, Garrett graduated from flying school at the Royal Australian Air Force base at Point Cook; he became a commercial pilot in 1927, and joined the Citizen Air Force. Garrett later became the first civilian instructor in the CAF. Garrett was as keen on gliding as he was on flying aeroplanes. In 1928, he set a British Empire record for gliding duration. In 1929, he founded the Gliding Club of Victoria.