Sergeant Major Fontenot enlisted in the U. S. Marine Corps in 1997 and recruit training at Marine Corps Recruit Depot San Diego, California, June 1997. Upon graduation, he reported to School of Infantry West, Camp Pendleton, California where he was assigned and trained as a 0351 Infantry Assaultman. Upon graduation, he reported to Basic Security Guard School in Chesapeake, Virginia.

In January 1998, he was assigned to Marine Corps Security Force Company, Bangor, Washington and served as a Security Guard. In February 2000, he was promoted to the rank of Corporal and executed orders to Second Battalion Seventh Marines Golf Company where he served as an Infantry Assualtman Section Leader participating in a work-up for deployment to Okinawa, Japan. Upon return from deployment, he reenlisted and accepted orders to The Basic School, Quantico, Virginia. There he instructed officers in basic small arms weapons as well as Infantry Assualtman tactics and techniques. After two years, he was promoted to Sergeant and given orders in August 2003 to First Battalion Fourth Marines, Camp Pendleton, California. In May 2004, he forward deployed to Iraq in support of Operation Iraqi Freedom II. While deployed, he conducted numerous combat missions and assisted in training the Iraqi Army. He also served forward deployed again during operation Inherent Resolve in 2006.

In December 2006, now promoted to Staff Sergeant, he reported to the School of Infantry West, where he served as Platoon Commander, Bravo Company, Infantry Training Battalion training Infantrymen. He also served as a Combat Hunter Instructor at Advanced Infantry Training Battalion. After being promoted to Gunnery Sergeant in February 2009, he was selected to serve as Chief Instructor for the 0351/0352 Leaders Course.

In December 2009, he reported to First Marine Division G-3 serving as the Current Operations Chief forward deployed in January 2010 while in support of Operation Enduring Freedom, Afghanistan. In February 2012, he conducted a work-up and deployment to Okinawa, Japan with Fox Company, Second Battalion First Marines as a Weapons Platoon Sergeant and eventually serving as the company Gunnery Sergeant. While on deployment he participated in Korea Military Exercise while on the 31st MEU enhancing the ROK Marines infantry techniques and tactics, and participated in training alongside the Philippine Marines in Rubber Craft Operations. June 2013, he reported to Second Battalion Third Marines assigned to Headquarters and Service Company as the S-3 Training Chief and then Company Gunnery Sergeant. Upon returning from deployment, he was transferred to Headquarters Battalion, Kaneohe Bay as the Operations Chief at Pu'uloa Range Training Facility.

In December of 2014, he was selected to the rank of First Sergeant and received orders to Marine Corps Security Force Battalion, Bangor Washington. There he served as Alpha and Headquarters and Service Company First Sergeant under the Strategic Weapons Security Program. January 2018, he received orders to CLR-15, 1st Maintenance Battalion, Reparable Management Company where he served as the Company First Sergeant, as well as in Headquarters and Service Company.

In July 2019, he was promoted the rank of Sergeant Major and received orders to VMGR-352, a C-130 squadron. January 2021, Sergeant Major Fontenot executed orders and assumed his current duties as the Inspector & Instructor Sergeant Major of Combat Logistics Battalion 23.

Sergeant Major Fontenot's personal awards include the Navy and Marine Corps Commendation Medal (gold star in lieu of fourth award), the Navy and Marine Corps Achievement Medal (gold star in lieu of second award) and the Combat Action Ribbon.