 He was educated at Haileybury and the Royal Military College, Sandhurst.Deedes was commissioned onto the unattached list of the Indian Army on 29 January 1910 and posted to the 31st Punjabis on 5 March 1911.In 1914 he was attached to the 57th Rifles in France and Belgium, where he served from 5 November 1914 to 25 September 1915.