Clark joined the Royal Australian Navy as a Cadet Midshipman in 1969. He graduated from the RAN college with a Bachelor of Science from the University of New South Wales, then served on eight ships before leaving the navy in 1979. He holds an MA from Oxford and a PhD from the University of New South Wales. He took several positions at UNSW, culminating in Director of the Australian Research Council Centre of Excellence for Quantum Computer Technology, before taking on the role of Chief Defence Scientist.