Following Pakistan's independence in 1947, Matinuddin was commissioned as a gunner in the 7th Field Regiment of the Royal Pakistan Artillery. He participated in the First Kashmir War, shelling enemy positions in the Bhimber sector. He studied at the Canadian Army Command and Staff College in Kingston, graduating in 1957. During his 34-year long service in the military, Matinuddin held various staff, instruction and command-related appointments, including heading an infantry division and assuming responsibility for operational planning as the Director General Joint Staff. He witnessed action in the Second Kashmir War and the 1971 War. In 1981, Matinuddin retired as a lieutenant-general from the Pakistan Army.