Sergeant Major Callahan is a native of Tampa, Florida. He enlisted in the Marine Corps in September of 2006, and attended Recruit Training at Marine Corps Recruit Depot, Parris Island, South Carolina. Following Recruit Training and Marine Combat Training, Private Callahan was assigned to Marine Corps Communication-Electronics School, Twentynine Palms, California, for certification as a 0612, Field Wireman.
Following MOS school, Private First Class Callahan executed orders to 1st Battalion, 9th Marines, Camp Lejeune, North Carolina, in April 2007. During his time with 1st Battalion, 9th Marines, he served as a Field Wireman and Wire Supervisor. He deployed to Ramadi, Iraq, and with the 24th Marine Expeditionary Unit.
In September 2010, Sergeant Callahan received orders to The Basic School, Quantico, Virginia. While there, he served as a Field Wireman, Field Radio Operator, Communications Instructor, and Company Operations Chief.
In September 2012, Sergeant Callahan received orders to 1st Battalion, 11th Marines. Sergeant Callahan served as the Battery Communications Chief for Battery C. During this time, Sergeant Callahan was a part of multiple exercises to include Operation Steel Knight, Desert Scimitar, Integrated Training Exercise, Regimental Fire Exercises, and Battalion Fire Exercises.
In 2014, Sergeant Callahan requested orders to the Marine Corps Recruit Depot, San Diego, California. Upon graduation from Drill Instructor School, Class 4-14, he was assigned to Hotel Company, Second Recruit Training Battalion. On 1 December 2014, Sergeant Callahan was promoted to the rank of staff sergeant. While on the Recruit Depot, Staff Sergeant Callahan served as a Drill Instructor, Senior Drill Instructor, and Water Survival Instructor. While serving as a Senior Drill Instructor, Staff Sergeant Callahan was selected as the 2017 MCRD San Diego Drill Instructor of the Year, which earned him a meritorious promotion to the rank of gunnery sergeant.
In January 2018, Gunnery Sergeant Callahan executed orders to Marine Wing Communications Squadron 28, aboard MCAS Cherry Point, North Carolina. Gunnery Sergeant Callahan served as the Headquarters and Service Company, Company First Sergeant.
In February 2020, Gunnery Sergeant Callahan executed orders to the Staff Noncommissioned Officer Academy, MCB Hawaii. During his time, he served as a Faculty Advisor, Senior Faculty Advisor, Master Faculty Advisor, and the Staff Noncommissioned Officer in Charge of Sergeants' School. Gunnery Sergeant Callahan was selected to first sergeant in December 2021. He was frocked to the rank of first sergeant in March 2022 and executed orders to MCRD Parris Island.
First Sergeant Callahan served as the Company First Sergeant for Bravo Company, Echo Company, and Sierra Company. First Sergeant Callahan was selected to the rank of sergeant major in November 2024 and was frocked to his current rank in May 2025.
Sergeant Major Callahan is currently serving as the Command Senior Enlisted Leader for Combat Logistics Battalion 453.
Sergeant Major Callahan is married and has two children. Sergeant Major Callahan has a B.A. History degree from Columbia College and an M.S. Social Science, History degree with Troy University. Sergeant Major Callahan's personal decorations include the Meritorious Service Medal, Navy and Marine Corps Commendation Medal, gold star in lieu of third award, and the Navy and Marine Corps Achievement Medal, gold star in lieu of third award.