In 1973, Brigadier-General O'Brien enrolled as a Private in 1 Montreal Militia Service Battalion where he worked as a driver until transferring the next year to 3rd Battalion, The Black Watch (Royal Highland Regiment). While at The Black Watch, Brigadier-General O'Brien served as an Infantry Rifleman, laying the foundation for a long career as a Militia Infantry Soldier and Officer.
Moving to Calgary in 1976, Brigadier-General O'Brien transferred to The Calgary Highlanders where he served for four years including a six-month tour with the United Nations Disengagement Observer Force Middle East in Golan Heights. In 1979, he moved to London and transferred to the 4th Battalion, The Royal Canadian Regiment (4 RCR).
On 14 December 1981, he received his commission to Second Lieutenant. As an officer in 4 RCR, he has served in virtually every position available in the Battalion. As a Lieutenant, in July 1983, he was given the honour of carrying the 4 RCR Colours at the Royal Canadian Regiment Centennial Trooping of the Colours presided over by Prince Phillip, Colonel-in-Chief of the RCR, in London, Ontario.
During the First Gulf War he was deployed in his civilian occupation to support the US Marine Expeditionary Force in operations in Kuwait. He received his promotion to Major in January 1993 and, on 12 June 1997 he was promoted to Lieutenant-Colonel and appointed Commanding Officer of 4 RCR. He also served as the Commanding Officer of the Infantry Battle Group for 31 Brigade in 1998. After turning over command of 4 RCR on 27 January 2000 he was appointed Deputy Commander 31 Canadian Brigade Group and on 25 August 2001, he was promoted to Colonel and appointed Brigade Commander.
After a highly successful tour of duty at 31 Canadian Brigade Group, including commanding 3 Light Brigade Group at Exercise Stalwart Guardian 2003, Brigadier-General O'Brien relinquished command on September 20th, 2003, and was appointed Assistant Chief of Staff Operations at LFCA HQ. He was promoted to his current rank on 19 February 2005 and appointed Deputy Commander Land Force Central Area at that time.
In March of 2006 he deployed to Afghanistan where he served as the Deputy Commanding General, Political Military Integration, in the Coalition Headquarters of Combined Security Transition Command – Afghanistan for nine months. While in Afghanistan he was responsible for the Coalition efforts in reform of the Afghan National Police, Political Military Integration and was appointed the senior NATO Liaison Officer for the Command. Upon his return to Canada he was appointed Director General Land Reserve.
Brigadier-General O'Brien's civilian occupation is in Business Development and Program Management with General Dynamics Land Systems Canada where he has participated in the Canadian and Australian LAV projects and led the New Zealand Light Armoured Vehicle Program. Brigadier-General O'Brien is an active member of the Canadian Infantry Association; he enjoys military history and golf.
