A doctor with the Royal Army Medical Corps (RAMC) during World War II, Ken Stewart saw distinguished service during the allied invasions of Sicily and southern Italy; at the Normandy landings; and with the forces entering Berlin following the Nazi surrender.

After the war he was deeply concerned about the need for post-war reconstruction in Europe and, instead of returning to Britain as a GP, he based in Italy for 10 years as a volunteer with Moral Re-Armament (MRA, now named Initiatives of Change), which had opened its centre for reconciliation in Caux, Switzerland, in 1946.