He returned to Australia in 1903 and joined the militia garrison artillery in New South Wales. In April 1904, he was commissioned as a lieutenant in the Royal Australian Artillery. In 1910, he was the first Australian to attend the Staff College at Quetta, now in Pakistan.[2]
Harrison married Roma Wingfield Zilla Clarke in November 1920. He was appointed commandant of the R.M.C. in January 1929 and promoted colonel in July. He retired from the army in January 1931 and took up farming on the Mornington Peninsula.[2]
In August 1940, Harrison was recalled from the reserve and reappointed as commandant of the R.M.C. until his retirement in January 1942. He died in Melbourne, survived by his wife, a son and a daughter. His son, Brian was the member for Maldon in the British House of Commons from 1955 to 1974.[2]