[1] Harrison was educated at Kilkenny College in Ireland and then at Mountjoy School, Dublin, before entering the Royal Military Academy, Woolwich.

He was commissioned into the Royal Engineers as a second lieutenant on 26 May 1916 and afterwards undertook the Young Officers' Course at the University of Cambridge.

[4] Harrison was mentioned in dispatches on 29 April 1941 for service on the battlefield, by this time his promotion to lieutenant-colonel had been confirmed (in a temporary rank).

[14] Harrison was sent to Tanganyika (now Tanzania) in East Africa as general manager of the Tanganyika groundnut scheme, a project to cultivate peanuts across vast areas of the territory and parts of British Kenya (modern-day Kenya) and Northern Rhodesia (Zambia), with the intention of extracting oils in order to reduce shortages in Britain in the aftermath of the war.

Their older son, Lieutenant Richard John Michael Harrison, was commissioned into the Coldstream Guards; he was killed in action serving in north west Europe in 1945 at the age of 20.