Major Donlin was commissioned as a 2ndLt in the United States Marine Corps in August 2005, through the Officer Candidates Course, and reported to The Basic School in Quantico, Virginia. In March 2006, he reported to Pensacola, Florida for primary flight training at Naval Air Station (NAS) Whiting Field. He then reported to NAS Meridian, Mississippi in April 2007 for advanced jet training.
He was designated as a Naval Aviator in May 2008, and reported to Marine Corps Air Station Cherry Point, North Carolina for follow-on training in the AV-8B Harrier attack jet. In October 2009, he reported to Marine Attack Squadron (VMA) 223, MCAS Cherry Point, for duty as an operational AV-8B Harrier pilot.
In February 2010, he joined VMA-542 and deployed in support of the 31st Marine Expeditionary Unit in the Marine Corps' Southeast Asia area of responsibility. While in VMA-542, he served as the Squadron Logistics Officer and Powerline Division Officer.
In January 2012, he reported to Naval Base Little Creek, Virginia for Tactical Air Control Party training, earning an Additional Military Occupational Specialty (AMOS) of Joint Terminal Attack Controller/Forward Air Controller (JTAC/FAC). In February 2012, he reported to 2D Tank Battalion, Camp Lejeune, North Carolina for duty as Bravo Company Forward Air Controller.
In July 2012, he deployed with Bravo Company in support of Operation Enduring Freedom to Helmand Province, Afghanistan, where he served as Tank Crewman/Loader and Forward Air Controller.
Upon return from deployment in January 2013, he was selected for the Marine Corps' Secondary Education Program (SEP), Leadership Education and Development (LEAD) track at the United States Naval Academy (USNA), earning a Masters in Leadership Education and Development. Major Donlin then served as the Company Officer for 28th Company, US Naval Academy, May 2014 through June 2016.
In July 2016, Major Donlin was selected to transition to the 7315 PMOS. He reported to VMU-2 in August 2016, and has served as the Operations Officer, Aircraft Maintenance Officer, and Executive Officer.
Major Donlin's awards include the Meritorious Service Medal, the Navy and Marine Corps Commendation Medal with Combat Distinguishing Device, the Navy and Marine Corps Achievement Medal, Combat Action Ribbon, and various campaign, service, and unit awards.