LtCol Derek Rey received his commission through the Naval Reserve Officer Training Corps at the University of Southern California in 2006. After completing the Basic Officer Course and Infantry Officer Course, he was assigned the military occupational specialty of Infantry Officer.

In 2007, 2ndLt Rey reported to 1st Battalion, 7th Marines, in Twentynine Palms, CA. He deployed in 2007 as a rifle platoon commander to Hit, Al Anbar province, Iraq, and in 2008 as an advisor to the Iraqi Marines to Umm Qasr, Al Basrah province, Iraq, in support of Operation Iraqi Freedom. Upon his return in 2009 1stLt Rey served as Battalion Training Officer and Assistant Operations Officer.

In 2010, 1stLt Rey reported to Bravo Fleet Antiterrorism Security Team (FAST) Company, Marine Corps Security Force Regiment, in Yorktown, VA, where he was promoted to Captain. While serving as a FAST platoon commander, he led the platoon through exercises and deployments to Panama, Guantanamo Bay, Japan, and throughout the US 7th Fleet's area of responsibility while embarked on the USS Blue Ridge. He also served as Executive Officer and subsequently Commanding Officer of Bravo FAST Company before leaving active duty in 2013.

Upon joining the Marine Corps Reserve, he served as a platoon commander in 3d Battalion, 25th Marines and 1st Battalion, 24th Marines before being promoted to Major. In 2017, he assumed command of Headquarters and Service Company, 2d Battalion, 25th Marines and later that year assumed command of Fox Company, 2d Battalion, 25th Marines. In 2019, Maj Rey led Fox Company through pre-deployment training and mobilized the Company to active duty. While activated, the Maj Rey commanded the Company during its deployment as Security Force Company, Task Force Southwest, in Helmand province, Afghanistan, in support of Operation Freedom's Sentinel and the NATO Resolute Support Mission.

In 2020, Maj Rey reported to 4th Air Naval Gunfire Liaison Company (ANGLICO), where he served as Operations Officer. In 2022, Maj Rey reported to 2d Battalion, 25th Marines, where he currently serves as Battalion Executive Officer. He was promoted to Lieutenant Colonel in 2023 prior to assuming command of 4th ANGLICO.

LtCol Rey is a graduate of several military schools and courses, including the College of the Naval Command and Staff and the Joint and Combined Warfighting School. LtCol Rey's personal awards include the Meritorious Service Medal, Joint Service Commendation Medal, Navy and Marine Corps Commendation Medal with combat "C" device and gold star in lieu of second award, and the NATO Meritorious Service Medal. He holds a Bachelor of Arts from the University of Southern California, a Master of Arts from Gonzaga University, and a Master of Business Administration from the University of Virginia’s Darden School of Business.