On 1 December 1941 Ewald volunteered for military service. After his pilot training, which included flight training with the Fliegerausbildungsregiment 23 in Kaufbeuren, he was posted, in the fall of 1943, to 6./JG 52 on the Eastern Front and was soon one of the best young pilots of his group. He accompanied Gerhard Barkhorn (301 victories), on over 100 missions as a wingman. On his fourth sortie, and on his first enemy encounter, he shot down his first opponent on 11 December 1943. He was awarded the Iron Cross 2nd Class, on 8 January 1944; the Iron Cross 1st Class on 7 March. He was promoted to leutnant on 1 May, and he received the Ehrenpokal der Luftwaffe on 25 May.
On 24 June 1944 he was shot down and wounded in Romania, but saved the parachute. In October, he returned to the front in Hungary, where he received the German Cross in gold on 30 November. On 1 March 1945 he was shot down by his own anti-aircraft guns. Fortunately, he was rescued unscathed. On 3 April his engine was hit while carrying out low-level attacks on Russian positions. He made a forced landing between the lines. He achieved his last victory (a Yak-9), on 16 April. Four days later he was awarded the Knight’s Cross of the Iron Cross.
Heinz Ewald reached 84 victories in 395 combat missions, 82 (plus 15 unconfirmed), on the Eastern Front, including 14 Il-2 Sturmoviks. He was held as a Prisoner of War at Fürstenfeldbruck Lager from 8 May until 22 June 1945.