Mark pursued a military career between 1971 and 1990. Mark initially served in the New Zealand Army. His first unit was the Royal New Zealand Electrical and Mechanical Engineers before moving to 2/1 Battalion, 3 and 10 Tpt Regiments and Queen Alexandra's Mounted Rifles before passing New Zealand Special Air Service selection. Mark served a 13-month tour of duty in the Sinai with the Multinational Force and Observers in 1982–83. After being refused entry into the NZSAS, he was contracted to the Sultanate of Oman as a technical staff officer from 1985 to 1986, and then joined the Sultan of Oman's Armed Forces becoming an electrical and mechanical engineering officer in the Sultan's Special Force Electrical and Mechanical Engineers between 1986 and 1990.