Lieutenant Colonel O'Brien is a native of Iowa City, Iowa, he graduated in 1988 from Moline Senior High School, in Moline, Illinois and enlisted in the Marine Corps and attended Recruit Training in San Diego, California in August of that same year.
After completing Recruit Training, he attended the Aviation Electronics School in Millington, Tennessee then reported to Marine Light Attack Helicopter Squadron 169 as a UH-1N and AH-1W avionics/electronics/weapons technician. While assigned to this unit, he deployed to Okinawa, Japan as part of the unit deployment program, supported Team Spirit 1990 and deployed in support of Operations Desert Shield and Desert Storm in 1990 - 1991. In 1993, he deployed to Mogadishu, Somalia in support of Operation Restore Hope as the senior military Nite Eagle FLIR technician. His billets while attached to this unit were Collateral Duty Inspector, shift supervisor, AH-1W test crew, UH-1N Door Gunner and qualified UH-1N Crew Chief.
In 1993, he was accepted to the Marine Enlisted Commissioning Education Program and attended the University of Illinois, Urbana-Champaign, and graduated in 1997. After attending The Basic School, he reported to Assault Amphibian Officers course in Camp Pendleton California then transferred to 2d Assault Amphibian Battalion, Camp Lejeune and served as an Amphibious Assault Vehicle platoon commander. In July of 2000, he deployed as the AAV platoon commander with Battalion Landing Team 2/2, 26th Marine Expeditionary Unit (SOC) upon his return was reassigned as the Executive Officer, Company A, 2d Assault Amphibian Battalion.
In May of 2001, he transferred to the United States Naval Academy to attend the Leadership and Education Development program, after completing the program he served as Plebe Summer Company Officer, 14th Company Officer, Leatherneck Platoon Commander, and academic instructor as well as a member of the Marine Corps Officer Selection board from June 2002 till June 2004.
In September 2004 he assumed command of Company B, 2d Assault Amphibian Battalion and deployed in March of 2005 in support of Operation Iraqi Freedom 04-06 supporting Regimental Combat Team 8. In November of 2005 he assumed command of Company D, 2d Assault Amphibian Battalion and deployed in March 2006 in support of Operation Iraqi Freedom 05-07 supporting Regimental Combat Team 5.
In November 2006 he assumed the duties as Operations Officer, Program Manager, Advanced Amphibious Assault Program office until his attendance at the Marine Corps Command and Staff College in June 2010. In August 2011 he deployed in support of Operation Enduring Freedom as the Regimental Combat Team 5, Afghan National Security Force Cell Leader. In September 2012 he was assigned as the Executive Officer, 3d Assault Amphibian Battalion. In June 2013 he deployed to the United Arab Emirates as the Deputy, Marine Corps Training Mission – United Arab Emirates. In November 2014, he assumed the duties as Executive Officer, Headquarters Battalion, 1st Marine Division. In June 2015 he assumed command of 3d Assault Amphibian Battalion, 1st Marine Division.
Lieutenant Colonel O’Brien was promoted to his present grade on the 1st of November 2013, and holds a Bachelors of Science degree from the University of Illinois and a Masters of Science degree in Leadership and Human Resource Development from the Naval Postgraduate School and a Masters of Military Science from the Marine Corps University.