After the war, McKinnon remained in Italy with a brigade group which was intended to serve in Japan with
J Force, the New Zealand contribution to the occupation of Japan. J Force shipped out to Japan in November 1945, where he was the group's Chief Administrative Office.In the
1947 King's Birthday Honours he was appointed an
Officer of the Order of the British Empire. He attended the Joint Staff College in the United Kingdom in 1948 and then commanded the Southern and Northern Military Districts. In 1953, McKinnon was awarded the
Queen Elizabeth II Coronation Medal. After a three-year period in
Washington, D.C., as head of New Zealand's Joint Services Staff, McKinnon was appointed adjutant-general of the New Zealand Army in 1958. Three years later, in the
1961 Queen's Birthday Honours, he was made a
Commander of the Order of the British Empire. The following year, he was made quartermaster-general and then in 1965, he was appointed Chief of the General Staff. In this role he persuaded the government to send an artillery battery to serve in the
Vietnam War. He retired from the army in 1967 having been made a
Companion of the Order of the Bath the
previous year. ==Later life==