Sergeant Major Mejia enlisted in the Marine Corps in September 2001 and completed recruit training at MCRD San Diego.
Following recruit training, Private First Class Mejia attended School of Infantry at Camp Pendleton, CA and subsequently promoted to the rank of Lance Corporal. There he was given orders to 3rd Bn 7th Mar at Twenty- Nine Palms, CA, and was assigned MOS 0311 Basic Rifleman.
Lance Corporal Mejia reported to 3rd Bn 7th Mar in February 2002. He was deployed to Liberation of Iraq 2003, filling the billet of Radio Operator and Squad Leader. He was then promoted to the rank of Corporal following his deployment to Iraq. Corporal Mejia was then deployed to Transition of Iraq and Iraqi Governance 2004, filling the billet of squad leader. He promoted to the rank of Sergeant in 2005 and deployed to National Resolution 2005, filling the billets of Platoon Guide and Platoon Sergeant. Sergeant Mejia was again deployed
to Iraqi Surge 2007, filling the billet of Fixed Site Security Officer.
Sergeant Mejia received orders in 2008 to Weapons and Field Training Battalion Camp Pendleton, and reported there as a Range Coach. He then promoted to the rank of Staff Sergeant in 2009, filling the billet of Platoon Sergeant for Delta Range.
In 2011 Staff Sergeant Mejia received orders to 3rd Bn 3rd Mar as a Platoon Sergeant. He deployed to Afghanistan Transition I in the same year. In 2013 he then redeployed to Marine Rotational Forces Darwin. In 2014 Staff Sergeant Mejia received orders and reported to 3D Light Armored Reconnaissance Bn at Twenty-Nine Palms.
In 2015 he deployed with his unit to Camp Schwab Okinawa, Japan. Following the deployment he was selected for Individual Augmentation and deployed to the Republic of Georgia and then Afghanistan Freedom Sentinel 2016. He promoted to the rank of Gunnery Sergeant soon after in 2017, filling the billet of Operations Chief for Headquarters and Services Company. In 2018 Gunnery Sergeant Mejia received orders to MATSG-22 to serve as the Group's Training Chief. The following year he received his Associates of Arts at Saint Leo University in 2019.
He continued his education and received his Bachelor of Arts in Criminal Justice from Saint Leo University in 2021. Gunnery Sergeant Mejia was selected to the rank of First Sergeant and received orders to Marine Corps Security Force Kings Bay Georgia. In 2024 First Sergeant Mejia received orders to Marine Wing Support Squadron 373.
In 2025 First Sergeant Mejia was selected to the rank of Sergeant Major and received orders to Marine Light Attack Helicopter Squadron where he currently serves with his wife, Katherine. Sergeant Major Mejia's personal awards and decorations include the Meritorious Service Medal, Navy and Marine Corps Commendation Medal (x3) (1 w/"V" device), Navy and Marine Corps Achievement Medal (x4), and Combat Action Ribbon.