Major Keegan enlisted in the Marine Corps in August of 2001. After completing Infantry Training Battalion and Basic Security Guard School, he was assigned in April of 2002 to Marine Corps Security Forces Keflavik, Iceland. LCpl Keegan was transferred to 3d FAST Company in April of 2003 in Williamsburg, VA.
In June of 2004, LCpl Keegan was assigned to 3d Battalion, 5th Marines, and deployed in support of OPERATION IRAQI FREEDOM II and participated in OPERATION PHANTOM FURY from September 2004 to April 2005. In June of 2005, Corporal Keegan re-enlisted and got assigned to WFTBN, Edson Range, from 2005-2008. He was assigned as a Marksmanship Coach and Primary Marksmanship Instructor for recruits. While assigned to WFTBN, Sergeant Keegan attained his bachelor's degree in Business Management/Human Resources from Park University.
In July of 2008, Sergeant Keegan received orders to 2d Battalion, 3d Marines in Kaneohe Bay, HI. In November of 2008, he was accepted to the Enlisted Commissioning Program, and in March of 2009, he was commissioned as a Second Lieutenant.
After completing The Basic School and Infantry Officer Course in Quantico, Virginia, he reported to Alpha Company 2d Light Armored Reconnaissance Bn in Camp Lejeune, NC, in April of 2010. During his tour, he deployed with BLT 2/2 in support of the 22d Marine Expeditionary Unit (MEU) as the LAR Detachment Commander from March of 2011 to February of 2012. While deployed with the 22d MEU on the USS BATAAN and participated in OPERATION UNIFIED PROTECTOR, upon his return from the MEU, he was assigned as the executive officer of Bravo Company, 2d LAR Bn.
From August of 2012 to March 2013, Major Keegan was assigned to an Individual Augment Billet in support of OPERATION ENDURING FREEDOM. He was attached to NATO-Training Mission Afghanistan / Combined Security Transition Command as a Senior Watch Officer in the CJ33.
From April of 2013 to June of 2016, Major Keegan was assigned to Recruiting Station Kansas City as the Operations Officer. In August of 2016, he was assigned to Expeditionary Warfare School.
Upon completion of EWS, Captain Keegan reported to Third Battalion, First Marines, in May of 2017. He deployed as the Battalion's Fire Support Coordinator and Weapons Company Commander in July 2018 in support of the 13th MEU's WESTERN PACIFIC DEPLOYMENT 1-19 on the USS ESSEX.
In July of 2019 Major Keegan attended Command and Staff College and graduated May of 2020 before being assigned to Recruiting Station Saint Louis.