Ellwood graduated from Duntroon in 1990 and was commissioned into the Royal Australian Infantry Corps. His early career included postings as a platoon commander in the &lt;a href="2nd/4th%20Battalion%2C%20Royal%20Australian%20Regiment"&gt;2nd/4th Battalion, Royal Australian Regiment&lt;/a&gt; and as an instructor in field training and tactics at Duntroon, before he was seconded to the British Army from 1998 for a two-year exchange with the Irish Guards, then stationed in Germany. During the secondment he deployed as part of the NATO intervention in the Kosovo War in 1999, serving as second-in-command of an armoured infantry company in the King's Royal Hussars Battle Group. For his service in Kosovo, Ellwood was awarded a Commander British Forces Commendation. He returned to Australia as a company commander and operations officer in the &lt;a href="5th/7th%20Battalion%2C%20Royal%20Australian%20Regiment"&gt;5th/7th Battalion, Royal Australian Regiment&lt;/a&gt; (5/7RAR). Ellwood commanded B Company on operations in East Timor from October 1999 to April 2000, when 5/7RAR deployed with the International Force East Timor.