Mark O'Neill is an experienced Australian Army officer with operational experience in Somalia, Mozambique, Iraq and Afghanistan. He has been the Chief of Army Fellow at the Lowy Institute for International Policy, Joint Operations LO to the DFAT and an lecturer at the National Security College. In 2013 he earned a PhD from the UNSW. He is currently posted to Army HQ.

Major Donald commenced his career as an Army Reservist at the University of New South Wales Regiment in 2007 before transferring to the Regular Army in 2009. During his full-time career, he has served as an Operations Officer for Reserve Units on two occasions and as an Acting Brigade Major within a Reserve Formation. Major Donald assumed the role of Officer Commanding Arnhem Squadron, North West Mobile Force (NORFORCE) in January 2021.