During the Second World War, Coleman commanded the 4th Battalion, Welch Regiment from 1941 to 1944 and took over as acting commander of the 160th Infantry Brigade, his battalion's parent formation, in late 1943, before Brigadier Lashmer Whistler arrived in January 1944 to take command, with Coleman returning to commanding the 4th Welch. In June 1944 Coleman succeeded Whistler in command of the brigade, leading it throughout the campaign in North-West Europe from Normandy very nearly to the borders of Denmark by way of Falaise, Antwerp, Nijmegen, 's-Hertogenbosch, Wessem, the Ardennes, the Reichswald, the Rhine, the Weser, and Hamburg. He was awarded the Distinguished Service Order (DSO) in 1945 and the Dutch Knight 4th Class of the Military Order of William in 1947. As his brigade major wrote after his death, the respect the men of the brigade had for him "probably gave him as much pleasure and satisfaction as any of his later achievements". Certainly he wrote very warmly of the achievements of the 53rd (Welsh) Infantry Division, of which his brigade formed a part, in his preface to the history of its part in the Second World War, published in 1955, and as its author makes clear, he made a considerable contribution to this account.