Miguel Cortes Jr. is a native of San Benito, Texas and graduated from Port Isabel High School in Port Isabel, Texas, in 2002. Sergeant Major Cortes enlisted in the Marine Corps and reported to Marine Corps Recruit Depot (MCRD), San Diego, California, in 2002 for recruit training. Upon his graduation, he reported to Marine Combat Training at Camp Pendleton, California. He then attended his MOS school of Ground Communications Radio Repairman Course in Twenty-nine Palms, California, from October 2002 to March 2003, during which time he was promoted to Private First Class.

In March of 2003, he reported for duty to 1st Battalion, 7th Marines, Twenty-nine Palms, California as a Radio Repairman. In March 2003, he deployed to Iraq in support of Operation Iraqi Freedom (OIF). In August 2003, he was promoted to the rank of Lance Corporal. In July 2004, he was promoted to the rank of Corporal. In September 2004, he deployed to Iraq in support of OIF 2-2 as the Communications Maintenance Supervisor. In August 2005, he was promoted to the rank of Sergeant. In February 2006, he deployed to Iraq in support of OIF 5-7 as a Section Leader and Platoon Sergeant for the battalion commander's personal security detachment.

In January 2007, Sergeant Cortes reported to Weapons Field Training Battalion (WFTBN) West, Camp Pendleton, California. He served as the Billeting Chief for WFTBN West. In January of 2009, Sergeant Cortes attended his follow on MOS school at Twenty-nine Palms, California, for Communications Maintenance Chief's course. In February 2009, he was promoted to Staff Sergeant.

In October 2009, Staff Sergeant Cortes reported to 1st Reconnaissance Battalion, where he served as the Battalion's Communications-Electronics Maintenance Chief and the Electronic Key Management System Manager. In May 2010, Staff Sergeant Cortes deployed to Afghanistan in support of Operation Enduring Freedom (OEF) 1-0. In November 2011, Staff Sergeant Cortes deployed to Afghanistan for the second time in support of OEF 11.2-12.1.

In January 2013, Staff Sergeant Cortes reported to MCRD, San Diego, California for Drill Instructor School. Upon graduation in March, he was assigned to H Company and G Company, 2d Recruit Training Battalion. In July 2015, he was meritoriously promoted to the rank of Gunnery Sergeant. In January 2016, Gunnery Sergeant Cortes was transferred to Drill Instructor School, where he served as an Instructor.

In January 2017, Gunnery Sergeant Cortes reported to 3d Maintenance Battalion, Okinawa, Japan, and held the billet of Radio Repair SNCOIC. In May 2018, Gunnery Sergeant Cortes was transferred to General Support Maintenance Company, where he served as the Company First Sergeant. In January 2019, Gunnery Sergeant Cortes was promoted to First Sergeant and transferred to Engineer Maintenance Company, where he served as the Company First Sergeant. In August 2019, First Sergeant Cortes transferred to III Marine Expeditionary Force Support Battalion, where he served as the Company First Sergeant for Support Company.

In January 2021, First Sergeant Cortes reported to MCRD, San Diego, California. He served as the Company First Sergeant for Second Battalion, Company E, Company G and Support Battalion, Special Training Company. In January of 2023, he was promoted to Sergeant Major and reported to his current duty station of Camp Pendleton, California. He is assigned as the Detachment Sergeant Major for Marine Airwing Group-41, Detachment A.

Sergeant Major Cortes earned his Associate's Degree in General Studies and Bachelor's Degree in Homeland Security. His personal awards include the Navy/Marine Corps Commendation Medal (gold star in lieu of fourth award), Navy/Marine Corps Achievement Medal (gold star in lieu of third award).