McCormack was commissioned in 1963 and served in Malaysia and Singapore during the Indonesia–Malaysia confrontation, and subsequently took part in the Vietnam War. He served as commanding officer of No. 1 Squadron RAAF in the 1980s. He was made commanding officer of No. 82 Wing RAAF in 1987, Director General Force Development Air at Headquarters, Australian Defence Force in Canberra in 1989 and Air Attaché in Washington D. C. in 1993. In 1995 he became Commander for the Integrated Air Defence System at Butterworth in Malaysia.