Born the son of Arthur Blair and educated at Harrow School and the Royal Military College, Sandhurst, Blair was commissioned as a second lieutenant into the Seaforth Highlanders on 26 January 1939. He served in World War II with the 2nd and 7th Battalions of his regiment. Serving with the 2nd Battalion, which formed part of the 51st (Highland) Division, in 1940, the battalion was forced to surrender at Dunkirk, and he became a prisoner of war at the Oflag V-B camp at Biberach in Baden-Württemberg. He escaped to Switzerland and from there to Spain and to Gibraltar. As such he was the first officer to return home after escaping from a prisoner of war camp. Blair was awarded the Military Cross for his exploits. He later served with the 7th Battalion, Seaforths, which formed part of the 15th (Scottish) Infantry Division, and was with the battalion throughout the campaign in Northwest Europe, landing in Normandy shortly after D-Day in June 1944 and fighting until Victory in Europe Day almost exactly eleven months later.