Colonel Grimmett is a graduate of Gardner-Webb University and was commissioned in March 2002. After completing The Basic School and the Field Artillery Officer Basic Course in 2004, he reported to 2nd Battalion, 10th Marine Regiment, where he served as Guns Platoon Commander, Forward Observer, Fire Direction Officer, and Liaison Officer. During this tour, he deployed twice with the 22d Marine Expeditionary Unit: first to Kandahar Afghanistan with Battalion Landing Team (BLT) 1/6 in support of Operation ENDURING FREEDOM, and then to Hit, Iraq with BLT 1/2 in support of Operation IRAQI FREEDOM.
In July 2006, he reported to 5th Air Naval Gunfire Liaison Company (ANGLICO), serving as Firepower Control Team Leader and Supporting Arms Liaison Team OIC. While with 5th ANGLICO, he deployed twice to Al Anbar, Iraq in support of Operation IRAQI FREEDOM.
Following this tour, he attended Expeditionary Warfare School in Quantico, VA. After graduation, he reported to 5th Battalion, 11th Marine Regiment and assumed command of Headquarters Battery in September 2010. He later took command of Battery T and deployed to Afghanistan in support of Operation ENDURING FREEDOM, subsequently serving as the Battalion Operations Officer.
In 2013, he attended Command and Staff College in Quantico, earning a master’s degree in military studies. Upon graduation, he was assigned to Naval Sea Systems Command (NAVSEA) in Washington, D.C., serving with Program Executive Office (PEO) Ships, PMS 385, as the Marine Corps Liaison and Operational Test and Evaluation Project Officer.
In July 2016, he reported to 12th Marine Regiment, initially serving as Assistant Operations Officer. He then joined 3rd Battalion, 12th Marines as the Battalion Operations Officer, later returning to Headquarters Battery to serve as 3d Marine Division Assistant Fire Support Coordinator. He concluded his tour as Regimental Logistics Officer.
From 2019-2021, he served as commander 5th Air Naval Gunfire Liaison Company (ANGLICO), III MEF. After command, he was selected as the Commandant of the Marine Corps' Senior Fellow to the United States Agency for International Development (USAID). While at USAID he served as the senior military advisor to the Director for the Center for Conflict and Violence Prevention within the Bureau for Conflict Prevention and Stabilization.
In 2022, Colonel Grimmett reported to 3d Marine Littoral Regiment where he served as the Executive Officer, and upon promotion, was reassigned to the U.S. Pacific Fleet, where he served as the Director of Operations, Joint Fires and Effects Center, and Fleet Marine Officer.
In 2025, he assumed command of Headquarters and Service Battalion, U.S. Marine Corps Forces, Pacific, where he currently serves as the Commanding Officer.
Colonel Grimmett’s personal decorations include the Meritorious Service Medal with two gold stars in lieu of third award, the Navy and Marine Corps Commendation Medal with one gold stars in lieu of second award, the Navy and Marine Corps Achievement Medal with combat distinguishing device and two gold stars in lieu of third award, and the Combat Action Ribbon with one gold star in lieu of second award.