Lt. Col. Riordon was commissioned in May 2008. Upon completion of The Basic School and Combat Engineer Officer Course, Lt. Col. Riordon was assigned to 2d Combat Engineer Battalion, 2d Marine Division, Camp Lejeune, North Carolina. He assumed responsibilities as the 3rd platoon commander, Company C, 2d CEB and deployed in support of Operation ENDURING FREEDOM 11.1 with Third Battalion, Second Marine Regiment in February 2011. Following re-deployment, he was assigned as 2d CEB's assistant operations officer. In February 2012, he was assigned as the deputy officer in charge of a police advisor team. He deployed in support of Operation ENDURING FREEDOM 12.1 with Second Battalion, Seventh Marine Regiment. Following re-deployment, he assumed command of Company B, 2d CEB in January 2013.
In July 2013 he reported to TBS as an instructor. While at TBS, Lt. Col. Riordon served as the combat assault platoon commander, staff platoon commander and company executive officer. He reported to Expeditionary Warfare School in August 2016 and graduated in May 2017.
In June 2017 Lt. Col. Riordon reported to 8th Engineer Support Battalion, 2d Marine Logistics Group, Camp Lejeune, North Carolina. Lt. Col. Riordon served as the battalion S-4 officer from June 2017 to March 2018. He then served as the battalion operations officer from April 2018 to January 2019. In February 2019, he received orders to Combat Logistics Battalion 26 as the executive officer. He deployed with the 26th Marine Expeditionary Unit from December 2019 to June 2020.
Post redeployment, he reported to Marine Corps Command & Staff College, Quantico, Virginia in July 2020 and graduated in June 2021.
In July 2021, he reported to the LCE Division within Capabilities Development Directorate, Combat Development & Integration, HQMC. He worked in both the Engineer and Plans Branches within LCE Division.
In May 2024, he reported to the Command Element, II Marine Expeditionary Force, Camp Lejeune, North Carolina and served
as the Engineer Officer on staff within the G4. In June 2025, he assumed command of 8th ESB.