CWO Mario Grondin enrolled in the Canadian Armed Forces on 21 November 1989 as a reservist with the Royal New Brunswick Regiment in Edmundston, NB. While in the Army Reserve, he deployed to Bosnia from 1994 to 1995 with Juliet Coy 2 RCR as part of the RCD Battle Group on OP CAVALIER, followed by Haiti in 1997 as part of the 3 R22eR Battle Group on OP STABLE. Upon return to Canada, he transferred to the Regular Force, with his first posting being with 1 RCR in Petawawa, ON.

During his first posting in Petawawa, he completed two more deployments: OP KINETIC in Kosovo from 1999 to 2000 and OP PALLADIUM in Bosnia from 2003 to 2004. Later that summer, he was posted to the Infantry School in Gagetown, NB, and the following year, after his promotion to the rank of Sergeant, he was posted to Edmundston, NB as a Regular Force Support Staff with his old reserve unit. In 2007, he returned to Petawawa with the third Battalion, The RCR. During that time, he completed the Infantry Platoon Second in Command Course and was posted to the first Battalion shortly after in order to deploy to Afghanistan from 2008 to 2009 with the Observer Mentor and Liaison Team (OMLT) as a newly promoted Warrant Officer.

In the summer of 2009, he returned to the Infantry School in Gagetown until his posting to 2 RCR in July 2014, where he assumed the position of Company Quartermaster until his promotion to MWO in July 2015. While employed as a CSM, he deployed along with two platoons from his company to the Middle-East on OP PROVISION, in order to facilitate the resettlement of 25,000 Syrian refugees to Canada.

Upon his return from Lebanon, he assumed the 2 RCR Ops MWO’s position until his posting to the Infantry School as the DSM/SI in July 2017. In July 2018, CWO Grondin was posted to the CDS Office in Ottawa as the Public Relations and Protocol MWO. He was promoted to his current rank and appointed as RSM of the Infantry School in June 2019. CWO Grondin was appointed Formation Sergeant Major of the Combat Training Center on 20 May 2021.

CWO Grondin was appointed to his current position as Formation Sergeant Major of the 5TH Canadian Division in July 2024.