In 1988, David Mason joined the French Foreign Legion. He stayed for five years and served in the Legion's elite Parachute Regiment. David later wrote about his time in the Legion in MARCHING WITH THE DEVIL. In 1998, alone with three camels, David walked across Australia at its widest point, carrying out the first recorded solo east-to-west crossing of the Simpson Desert. For this expedition he was awarded the Gold Medal of the Australian Geographic Society. He wrote a book about this journey titled, WALK ACROSS AUSTRALIA: THE FIRST SOLO CROSSING.
For a decade David was Counsel, International Law in the Department of Defence. He was Senior Adviser to Australia's Defence Minister and later, National Security Adviser to the Attorney-General of Australia. David left the Attorney's office to pursue a Doctorate in Law at the Australian National University's College of Law. His doctoral thesis deals with the status of mercenaries in international armed conflict. David has deployed on operations eight times and is the only person to have served as a Legionnaire, Australian Defence Civilian on Bougainville and in Iraq, Private Contractor in Iraq and as an Australian Defence Force Officer in Afghanistan.