In October 1917, Johnston became upset when he was superseded by Brigadier General Walter Adams Coxen for the post of Corps Artillery commander on 18 October 1917 and asked to be sent home. General William Birdwood accepted the request, he was replaced by Brigadier General Owen Phillips on 1 November 1917 and returned to Australia. For his services on the Western Front, Johnston was appointed a Companion of the Order of the Bath (CB) and Companion of the Order of St Michael and St George (CMG); he had been Mentioned in Despatches four times.