Sergeant Major Jairo A. Fredonis enlisted in the Marine Corps in June 1998 and attended recruit training at Marine Corps Recruit Depot, Parris Island, South Carolina. He graduated Company Honor-man and was meritoriously promoted to Private First Class. Upon completing boot camp, he reported to the School of Infantry, Camp Geiger, North Carolina, and received the MOS of 0311 and 0341, mortarman. He reported to 1st Light Armored Reconnaissance Battalion (LAR), Camp Pendleton, California.

While serving with 1st LAR, he deployed with Charlie Co, Battalion Landing Team 1/4, 15th Marine Expeditionary Unit, Special Operations Capable from January 2000 to July 2000. He redeployed with 1st LAR to Iraq in support of Operation Iraqi Freedom One in 2003. He was assigned as 81mm Mortar section leader as a part of Regimental Combat Team 5. Upon completion of his deployment in Iraq, He reported to 3d Battalion 3d Marines, Weapons Co, 81mm mortar platoon, Marine Corps Base Hawaii.

In 2004 he deployed with 3d Battalion 3d Marines to Afghanistan in support of Operation Enduring Freedom from November 2004 to June 2005. He then redeployed as the Platoon Sergeant for 3d Battalion 3d Marines Weapons Company Mobile assault platoon 1, in the Al-Anbar province, Iraq during Operation Iraqi Freedom 5-07, from March 2006 to October 2006.

Upon his return, he checked into School of Infantry West, Camp Pendleton, California, where he completed Marine Combat Instructors Course and was assigned to Infantry Training Battalion, Charlie Company, as 1st Platoon's Platoon Commander. He was then appointed as a primary instructor to Marine Combat Instructor School, where he was meritoriously promoted to Gunnery Sergeant.

In June 2010, He reported to the 2d Battalion 4th Marines, 5th Marine Regiment, and was assigned to the sniper platoon.  He held the billets of Scout Sniper Platoon Sergeant and Scout Sniper Platoon Commander throughout the Battalion's pre-deployment workup and deployment to Helmand Province, Afghanistan, from August 2011 to April 2012.

In June 2012, he reported to Marine Corps Recruit Depot, San Diego, and assumed the duties as the Headquarters Battalion's Operations Chief. While on the Depot, he was selected and promoted to First Sergeant. In March 2013, he reported to 3d Battalion, 7th Marines, and was assigned as the Weapons Company First Sergeant.  He deployed to Sangin District, Helmand Province, Afghanistan from, September 2013 to March 2014.  He deployed again with the Battalion from April to October 2015 in support of Special Purpose Marine Air-Ground Task Force  - Central Command's Task Force TQ as the Security force First Sergeant in Al-Taqqadum, Iraq.

He received orders to 6th Communication Battalion Inspector-Instructor staff, where he served as the Site First Sergeant for the Curtin-Garvey Complex in Brooklyn, New York. He was selected and promoted in February 2017 to Sergeant Major. Sergeant Major Fredonis was assigned to School Of Infantry West, where he was assigned as the Advanced Infantry Training Battalion, Sergeant Major.   In March 2021, Sergeant Major Fredonis was assigned orders to the 2d Low Altitude Air Defense Battalion where he severed until May 2023. He was then assigned orders to be Recruiting Station New York Sergeant Major.

Sergeant Major Fredonis' awards include two Meritorious Service Medals, three Navy Commendation Medals, four Navy and Marine Corps Achievement Medals, two with combat distinguishing devices, and two combat action ribbons.