SgtMaj O'Brian was born in New Orleans, LA and enlisted in the Marine Corps in January 2002. He attended Recruit Training at Parris Island, SC and graduated in March 2002 from 2nd Recruit Training Battalion, Golf Company, Platoon 2025. In April 2002, Private First Class O'Brian graduated from Marine Combat Training - East and reported to the Basic Low Altitude Air Defense (LAAD) Gunner School at Fort Bliss in El Paso, TX. Upon completion of the Basic LAAD Gunner School in September 2002, PFC O'Brian received orders to 3rd LAAD Bn., Camp Pendleton, CA and joined Alpha Battery as an Assistant-Gunner.
In October 2002, LCpl O'Brian was hand-selected as the Battery Marine of the Quarter and subsequently assigned to the LAAD Detachment, Marine Air Control Group-38 Detachment, HMM-163, 13th Marine Expeditionary Unit (MEU). In January 2003, LCpl O'Brian was selected as the Aviation Combat Element's Marine of the Quarter and was meritoriously promoted to the rank of Corporal in March 2003. While assigned to the 13th MEU, Corporal O'Brian participated in Operation Sweeney as part of Operation Iraqi Freedom. Upon return from the 13th MEU, Corporal O'Brian was assigned to the LAAD Detachment, Marine Air Control Group-38 Detachment, HMM-165, 15th (MEU). In October 2004, Corporal O'Brian was selected as the ACE NCO of the Quarter and was meritoriously promoted to the rank of Sergeant in November 2004.
As part of the 15th MEU, Sergeant O'Brian was assigned as part of the Personal Security Detachment for the MEU Commander and was part of various missions executed from Forward Operating Base Falcon in Baghdad, Iraq. Upon return from deployment in June 2005, Sergeant O'Brian was assigned to Bravo Battery, 3d LAAD Bn. as a Section Leader. In September 2006, Sergeant O'Brian was transferred to Marksmanship Training Branch, Wilcox Rifle Range and served as the Range NCOIC, Tower NCO, and Pits SNCOIC as part of the Fleet Assistance Program.
In January of 2007, Sergeant O'Brian was assigned to Alpha Battery, 3d LAAD Bn. as a Section Leader and deployed in August of that same year in support of Operation Enduring Freedom to Combined Joint Task Force - Horn of Africa, Camp Lemonier in Djibouti, Africa. In July 0f 2008, Sgt O'Brian reported to Drill Instructor School, Marine Corps Recruit Depot, Parris Island, SC. In October 2008, he graduated from DI School and was assigned as a Drill Instructor, 1st Recruit Training Battalion, Charlie Company. Sergeant O'Brian was promoted to the rank of Staff Sergeant in October of 2010. Upon completion of his tour where he served as a Drill Instructor and Senior Drill Instructor, Staff Sergeant O'Brian received order to 3d LAAD Bn. in March 2012.
From March 2012 to April 2017, Staff Sergeant O'Brian served as a Platoon Sergeant and Battery Operations Chief for Alpha Battery, the Battalion Logistics Chief, Logistics Officer, AA&E Officer, and Armory Officer, before returning to Alpha Battery as the Battery Operations Chief in April 2017.
Staff Sergeant O'Brian received orders to Officer Candidates School in April of 2018. He was promoted to the rank of Gunnery Sergeant in July of 2018. While at OCS, Gunnery Sergeant O'Brian served as a Platform Instructor, Instruction SNCOIC, and Curriculum SNCOIC as part of the Academics Section until he received orders to return to the Fleet Marine Force in August of 2021.
Gunnery Sergeant O'Brian arrived at 2d Low Altitude Air Defense Battalion and was assigned as the Battalion Logistics Chief, Headquarters and Service Battery. He was assigned the collateral duty as the Headquarters and Service Battery First Sergeant in October 2021 and was promoted to his current rank of 1stSgt in December of 2021. He served as the Unit Senior Enlisted Leader for Bravo Battery from December of 2021 until December of 2022 and as the Unit Senior Enlisted Leader for Charlie Battery, 2d LAAD Bn until January 2024. In January 2024, he assumed the duties as the Unit Senior Enlisted Leader for Bravo Company, Marine Air Support Squadron 1.
SgtMaj O'Brian was promoted to his current rank in March of 2025 and assigned to 5th Air Naval Gunfire Liaison Company, III MEF as the Command Senior Enlisted Leader.
SgtMaj O'Brian has a Bachelor's Degree in Business Finance from the University of Phoenix, and his personal awards include the Navy and Marine Corps Commendation Medal with two gold stars and the Navy and Marine Corps Achievement Medal with one gold star.