Roberts-Smith joined the Australian Army in 1996 at age 18. After completing basic training at Blamey Barracks in Kapooka, New South Wales, he underwent initial employment training at the School of Infantry at Lone Pine Barracks in Singleton, New South Wales. From there, Roberts-Smith was posted to the 3rd Battalion, Royal Australian Regiment (3 RAR) in Holsworthy, New South Wales. Initially part of a rifle company, he subsequently became a section leader in the Direct Fire Support Weapons Platoon. With 3 RAR, Roberts-Smith was deployed to East Timor twice, the first time as part of the International Force East Timor in 1999.