Julian Billmair enlisted into the Marine Corps on May 22, 2006. He graduated from Marine Corps Recruit Depot Parris Island as the honor graduate from Mike Company and was meritoriously promoted to Private First Class. Private First Class Billmair executed orders to Marine Combat Training Battalion, School of Infantry-East in Camp Geiger, North Carolina. Upon completion of his MOS school, Private First Class Billmair reported to 2d Marine Division as a combat photographer. In April of 2007, Lance Corporal Billmair deployed to Fallujah, Iraq in support of Operation Iraqi Freedom, attaching to II Marine Expeditionary Force, Regimental Combat Team 6, and Regimental Combat Team 2 units. Lance Corporal Billmair returned from Iraq in February 2008 before executing a lateral move to the 0311 MOS.
After completing Infantry Training Battalion, Corporal Billmair reported to 3rd Battalion, 7th Marines, Kilo Company where he served as an infantry squad leader. In March 2010 Corporal Billmair deployed to Musa Qalah and Sangin, Afghanistan in support of Operation Enduring Freedom. He was meritoriously promoted to Sergeant during the deployment in April 2010. Upon his return, Sergeant Billmair executed orders to be a Combat Instructor in July 2011 and was assigned to Marine Combat Training Battalion, India Company. He was meritoriously promoted to Staff Sergeant, 0369 Infantry Unit Leader on January 2, 2013. During his time as a combat instructor, he served as an Instructor Group platform instructor, platoon sergeant, and platoon commander.
In July of 2015, Staff Sergeant Billmair received orders to report to 1st Battalion, 4th Marines, Weapons Company where he was a section leader for 81mm platoon. In October 2015, he was transferred to 1st Battalion, 1st Marines, Charlie Company to serve as a weapons platoon sergeant for the Unit Deployment Program to Okinawa, Japan. In April 2016 Staff Sergeant Billmair then deployed to Australia as a rifle platoon sergeant in support of Marine Rotational Forces-Darwin. Upon his return in October, he received orders to the Staff Noncommissioned Officer Academy in Quantico, VA where he served as the Chief Faculty Advisor for Sergeants School. He was promoted to Gunnery Sergeant on September 1, 2017.
In June of 2019, Gunnery Sergeant Billmair reported to Tactical Training and Exercise Control Group (TTECG) where he served as an advanced maneuver coyote. In March of 2021, he was frocked to First Sergeant and received orders to Headquarters Company, Communications Training Battalion, Marine Corps Communication-Electronics School, where he served as a Senior Enlisted Advisor. In November 2022, First Sergeant Billmair received orders to Marine Wing Support Squadron 372, where he served as the Support Company Unit Senior Enlisted Leader, and deployed in support of Marine Aviation Support Activity in the Philippines. In April of 2025, First Sergeant Billmair executed orders to 1st Maintenance Battalion, where he served as the Unit Senior Enlisted Leader for Tactical Maintenance Company and Headquarters and Service Company. He is currently serving in the role of the 1st Maintenance Battalion Sergeant Major.