He spent most of the war on a variety of staff appointments, and married Victoire Marion Williams-Freeman in 1942. Promoted to lieutenant colonel, he was appointed as Commanding Officer (CO) of the 1st Battalion, Manchester Regiment, in March 1944. The battalion (formerly the 6th Battalion, a Territorial Army before being redesignated as 1st Battalion in May 1942), serving as the machine gun battalion of the 53rd (Welsh) Infantry Division, a first-line TA formation commanded by Major General Robert Ross, was poorly trained and virtually unfit for duty, but Harington quickly brought it to full combat readiness. The battalion, along with its parent division, landed in Normandy, France, in late June, three weeks after the Normandy landings, and was engaged in severe fighting throughout the Battle of Normandy, and most of the subsequent fighting in Western Europe, until Harington relinquished command in mid-September 1944, when he became a General Staff Officer Grade 1 (GSO1) with the 53rd Division HQ. He retained this post until May 1945. For his services as CO of the 1st Manchesters, Harington was awarded the Distinguished Service Order DSO in early 1945.