After graduating from Michigan State University, Lieutenant Colonel Eastin attended Officer Candidate School in Quantico, Virginia and was commissioned a Second Lieutenant in April 2000. After completing The Basic School and Infantry Officer Course, he was assigned as a rifle platoon commander in Company L, 3d Battalion, 4th Marines, and deployed as part of a Unit Deployment Program to Okinawa. In January 2003, he was assigned duties as the company executive officer, and conducted combat operations in support of Operation IRAQI FREEDOM I.
In September 2003, Lieutenant Colonel Eastin returned to Marine Corps Base Quantico, and was assigned to Security Battalion as the Battalion Legal Officer and Adjutant. Following his tour as an Adjutant, he began working in January 2006 as a Special Operations Officer, G-3, Training and Education Command (TECOM).
In August 2006, Lieutenant Colonel Eastin attended the Expeditionary Warfare School. Upon graduation he was assigned to 3d Battalion, 5th Marines to serve as the Commanding Officer, Company L. During this period, he led the company during combat operations in Fallujah, Iraq in support of Operation IRAQI FREEDOM 06-08. Upon the battalion’s redeployment, Lieutenant Colonel Eastin took command of Weapons Company and deployed to Okinawa as the Commander, Weapons Company, and the Fire Support Coordinator for the Battalion Landing Team with the 31st Marine Expeditionary Unit.
In August 2009 to July 2012, Lieutenant Colonel Eastin served as a Faculty Advisor at the Expeditionary Warfare School. During 2010, he was directed to report for a six-month tour, as part of the individual augment program, to USCENTCOM to serve as the Assistant Current Operations Officer, Special Activities Division to support Operations ENDURING FREEDOM and IRAQI FREEDOM. Upon completion of his last year on faculty, Lieutenant Colonel Eastin attended the Marine Corps Command and Staff College.
In August 2013, Lieutenant Colonel Eastin was assigned to serve as the Operations Officer, 1st Battalion, 9th Marines, and deployed to the Helmand Province, Afghanistan to participate in combat operations in support of Operation ENDURING FREEDOM 13.2. Upon his redeployment, he was reassigned as the Executive Officer, 2d Battalion, 8th Marines and deployed to Spain as the Detachment Commander, Ground Combat Element, Special Purpose Marine Air-Ground Task Force-Crisis Response-Africa 15.1, and the Executive Officer, Black Sea Rotational Force 15.1, headquartered in Romania. Upon returning to Camp Lejeune, he was assigned as the Acting Commander, 8th Marine Regiment while the Regiment deployed.
In August 2016, Lieutenant Colonel Eastin checked-in to Concept Development and Integration, Head Quarters Marine Corps to serve as the Infantry Capabilities Integration Officer.
In December 2016, Lieutenant Colonel Eastin reported to 3d Marine Regiment, and in February 2017 assumed command of 3d Battalion, 3d Marines.
Lieutenant Colonel Eastin’s personal awards include the Meritorious Service Medal with gold star, the Joint Service Commendation Medal, Navy and Marine Corps Commendation Medal with gold star, Navy and Marine Corps Achievement Medal with combat distinguishing device and gold star, and Combat Action Ribbon with gold star.