Colonel Fennell was commissioned a 2nd Lieutenant after graduating from Officer Candidate School in 1997. Under a law contract, he went on to complete his law and master’s degrees before graduating from The Basic School and Naval Justice School w/ honors in 2001. In 2002, he served as a Judge Advocate (JAG) at Marine Corps Base Hawaii as Officer in Charge of Legal Assistance and a Military Justice federal prosecutor. In 2004, Captain Fennell was honorably discharged whereupon he practiced corporate law and commercial litigation as a law firm associate attorney.
In 2006, hearing the call to serve in the War on Terror, Captain Fennell entered the Selected Marine Corps Reserve to join Marine Air Control Squadron 23 (MACS-23) in its upcoming deployment to Iraq. In 2007, he left civilian employment to complete the Air Defense Control Officer Course before deploying to Al Asad, Iraq in 2008 as Detachment Commander for the Tactical Air Operations Center (TAOC). He presented air command and control briefs on behalf of MACG-38 at U.S. Air Force Central Command in Qatar and 3D MAW at the Weapons and Tactics conference in Bahrain. After returning home, he was assigned Executive Officer of MACS-23.
In 2009, Major Fennell joined 4th Civil Affairs Group (CAG) to lead a civil affairs team in Helmand Province, Afghanistan. His team supported 3rd Battalion 10th Marines at Firebase Fiddlers Green in the shaping of Marjah before being re-assigned to 1st Battalion 6th Marines for Operation Moshturak. On February 13, 2010, Major Fennell led his team in the initial nighttime helicopter assault of central Marjah. He was later invited to brief an audience of international senior leaders at the Afghanistan Counter Insurgency Academy in Kabul, Afghanistan.
In September 2010, Major Fennell returned to MACS-23 as the TAOC Detachment Commander where he supported Exercise Northern Edge at Eielson Air Force Base, Alaska. In 2011 Major Fennell again served as Executive Officer, MACS-23 until the unit’s deactivation in September 2012. Combat Logistics Battalion 453 was activated in its place and Major Fennell was asked to remain as Executive Officer, CLB-453.
From 2013 to 2015, Lieutenant Colonel Fennell served as an Operations Watch Officer with U.S. Strategic Command, Joint Functional Component Command for Integrated Missile Defense (JFCC-IMD) in Colorado Springs, CO. In 2015, he was certified in MAGTF Information Operations and joined Marine Forces Pacific as the Information Operations Staff Officer where he supported U.S. Pacific Command exercises Pacific Sentry and Cobra Gold, Thailand. From April 2017 to May 2019, he had the honor of commanding Marine Tactical Air Command Squadron 48 (MTACS-48) at Naval Station Great Lakes, IL. He then attended the Naval War College in Newport, RI and was selected as an Arleigh Burke Fellow at the National Command College until graduating w/ distinction in 2020.
In August 2020, Colonel Fennell joined 3D MAW at Miramar, CA as the Reserve AC/S G-3 where he supported combined/joint exercises Pacific Sentry and Summer Fury. In March 2022, Colonel Fennell had the honor of assuming command of 1st CAG at Camp Pendleton, CA.
Colonel Fennell holds a B.S. degree from Colorado State University, M.S.E.L degree magna cum laude from Vermont Law School, M.A. degree w/ distinction from Naval War College, and J.D. degree from Lewis and Clark Law School. He enjoys supporting and volunteering at his local church, local elementary school, Veterans Service Organizations, and programs supporting children with special needs.