Zachary has worked for more than 40 years’ with populations affected by trauma, including refugees, asylum seekers, homeless youth, veterans, emergency service workers, and those affected by interpersonal and family trauma. He has published widely in the field of traumatic stress, From 2014-2024 he held the St John of God Chair of Trauma and Mental Health overseeing a 30 bed inpatient hospital service for PTSD. He has is a past president of the Australasian Society for Traumatic Stress Studies (ASTSS) and serves on the board of the NSW Service for the Treatment and Rehabilitation of Torture and Trauma Survivors (STARTTS). His research has influenced international policies, notably by articulating the detrimental mental health outcomes of stringent immigration laws and practices, including detention and temporary protection.