In 2001 Lieutenant Colonel Shields was posted as an Instructor at Rifleman Wing, School of Infantry, from which, he was promoted to Captain and posted as the Adjutant of the 11th/28th Battalion Royal Western Australia Regiment.

From 2004 to 2005 Lieutenant Colonel Shields was posted to the School of Armour as the Mechanised Officer Instructor, Tactics Wing, during which time he was awarded a Commandant Combined Arms Training Centre Commendation for excellence in the delivery of training. From January 2006 to August 2008 Lieutenant Colonel Shields was posted on exchange to the 1st Battalion Scots Guards (1SG), British Forces Germany. During his attachment to 1SG, Lieutenant Colonel Shields performed the roles of an Armoured Infantry Company Second Command and the Battalion Operations Officer. In November 2007 he was promoted to Major and deployed to Basra as the Scots Guards Battlegroup Warfare Officer. On deployment on Operation TELIC 11 he was responsible for planning and coordinating over 60 Battlegroup level operations including 27 combined joint strike operations in Basra. In recognition for his personal contribution to the British Mission in Southern Iraq, Lieutenant Colonel Shields was awarded as a Member of the Order of the British Empire (MBE).

On return from Iraq, Lieutenant Colonel Shields commanded B Company 5th Battalion from 2008 to 2009. In 2010 he completed Australian Command and Staff College attaining a Graduate Diploma in Management and Defence Studies from the University of New South Wales. Over 2011-2012 he was posted as the Senior Instructor Majors Team at the Officer Training Wing, where he led the development of the Majors Course and the Advanced Operations Course. In 2013, Lieutenant Colonel Shields was posted on promotion to Headquarters 1st Division / Deployable Joint Force Headquarters, as the Staff Officer Grade One Future Plans. During his time at the Deployable Joint Force Headquarters he led the development of five major regional contingency plans for Headquarters Joint Operations Command, led planning for OP PHILLINES ASSIST 2013 and led OP OKRA Build Partner Capacity plans for Iraq over 2014 to 2015. In 2014 Lieutenant Colonel Shields deployed as the Commander of the Australian Joint and Interagency Planning Team, and subsequent Chief of Staff of Joint Task Force 659 on OP HAWICK, where his team led planning and supported the coalition operation for the recovery of the victims of the MH-17 disaster in the Ukraine.

Lieutenant Colonel Shields holds a Bachelor of Behavioural Science from Griffith University, a Masters of Business (2013), and a Masters of Project Management from the University of New South Wales (2015). He is married to Evelyn and has two daughters, Sophia, born in November 2012, and Amelia born in October 2014. His interests include rugby, waterskiing, fitness and home improvement.

LTCOL Shields assumed Command of the 5th Battalion Royal Australian Regiment on 30 March 2015.