Field entered the Australian Defence Force Academy as an Australian Army officer cadet in 1984. He graduated with a Bachelor of Arts degree and, following additional training at the Royal Military College, Duntroon, was commissioned into the Royal Australian Infantry Corps. During his early career, Field served as a rifle platoon commander and mortar line officer in the &lt;a href="2nd/4th%20Battalion%2C%20Royal%20Australian%20Regiment"&gt;2nd/4th Battalion, Royal Australian Regiment&lt;/a&gt;, deployed for service with the United Nations Truce Supervision Organization in 1996–97, was adjutant of an Australian Army Reserve unit, served as an instructor at Duntroon, and commanded companies in the 2nd Battalion, Royal Australian Regiment (2RAR). He was operations officer when 2RAR deployed as part of the International Force East Timor in September 1999. For his "distinguished performance of duties" during the operation, Field was awarded a Commendation for Distinguished Service in March 2000.