After the First World War, Harrison remained with the British military, becoming adjutant of the Royal Military Academy, Woolwich from 1919 until 1921. He transferred from the Royal Marines to the British Army's East Yorkshire Regiment in 1924 and was brevetted lieutenant colonel in 1927. He then spent some years serving in different posts in Asia. He served in Singapore from March 1923 until April 1924, where he was General Staff Officer Grade 3 (GSO3) before being posted to British Malaya until 1925 as GSO 2. Between 1925 and 1928 he served as a GSO2 in the War Office. He was posted to India in 1930, becoming an instructor at the Staff College, Quetta, achieving the full rank of lieutenant colonel in 1932. That same year he was given a role in the Imperial Defence College and from 1932 until 1935 he commanded the 1st Battalion of the Green Howards. From 1935 to 1937 he was a GSO1 of British Troops in China. From 1937 to 1939 he was posted to Palestine, then the scene of an Arab revolt, and, promoted to temporary brigadier on 29 June 1937, he commanded the 14th Infantry Brigade in succession to Brigadier Henry Maitland-Makgill-Crichton. For his services in Palestine Harrison was twice mentioned in despatches, in December 1938, and again in April 1939. For his services whilst in the military Harrison was awarded the Order of the Sacred Treasure of Japan in 1926 and the Companionship of the Bath in 1939. He was still serving, during the Second World War, at the time of his death.