Lieutenant Colonel Greg Moynihan joined the Marine Corps after graduating from the United States Naval Academy in May 2008. Following his graduation, Lieutenant Colonel Moynihan reported to Company F, The Basic School in late June 2008, and graduated in January 2009.
Lieutenant Colonel Moynihan reported to 2d Battalion, 5th Marines in February 2009. While attached to 2d Battalion, 5th Marines, he deployed twice in support of the 31st Marine Expeditionary Unit (MEU) and conducted Operation KETSANA (Humanitarian Assistance in the Philippines in October 2009) and Operation TOMODACHI (Humanitarian Assistance in Japan in March and April 2011).
In August 2011, Lieutenant Colonel Moynihan reported to 1st Marine Regiment and assumed the duties of Regimental Adjutant. He was short toured at 1st Marine Regiment in order to join the 13th MEU in August 2012 as the MEU Adjutant. In August 2013, he deployed in support of the Western Pacific rotation in support of theater exercises and operations in 5th Fleet and 7th Fleet.
In July 2014, Lieutenant Colonel Moynihan reported to the Naval Postgraduate School. In March 2016, he graduated from the Naval Postgraduate School with a Master of Science in Management. His master’s thesis titled “Survival analysis of the modernized retirement system for the United States Marine Corps” received the Outstanding Thesis Award.
In May 2016, Lieutenant Colonel Moynihan reported to Manpower and Reserve Affairs (M&RA) in Quantico Virginia. Immediately after joined M&RA, he reported to Fort Gregg-Adams, Virginia, and attended the Operations Research, Systems Analysis – Military Applications Course (ORSA-MAC). He graduated ORSA-MAC with honors in August 2016. After reporting back to M&RA, he became the project lead for the Marine Corps’ Tailored Adaptive Personality Assessment System (TAPAS) and served as the Test Control Officer-in-Charge. In July 2018, he became the Aide-de-Camp to the Deputy Commandant for M&RA.
In July 2019, Lieutenant Colonel Moynihan reported to the Marine Corps Command and Staff College and graduated in May 2020 with a Master of Military Studies.
In July 2020, Lieutenant Colonel Moynihan reported to 1st Marine Logistics Group (MLG) and assumed the billet of the G-1 Operations Officer. While assigned to the 1st MLG, Lieutenant Colonel Moynihan was deployed to Arlington, Texas, in February 2021 to serve as the Officer in Charge of the Marine Corps’ first Vaccination Support Team. Lieutenant Colonel Moynihan’s team administered 166,225 Covid vaccinations to the residents of Tarrant County, Texas. Upon his return to Camp Pendleton in May 2021, Lieutenant Colonel Moynihan resumed his role as the G-1 Operations Officer.
In June 2022, Lieutenant Colonel Moynihan reported to 1st Marine Division. During his three-year tour, Lieutenant Colonel Moynihan served as the Deputy Assistant Chief of Staff G-1 from June 2022 to June 2024 and then served as the Assistant Chief of Staff G-1 from June 2024 to May 2025.
Lieutenant Colonel Moynihan’s personal decorations include the Meritorious Service Medal with gold star in lieu of fourth award, the Joint Commendation Medal, the Navy and Marine Corps Commendation Medal.