After commissioning as a second lieutenant in the US Army, Rubio became a UH-60 Blackhawk pilot. Rubio was a platoon leader in A Company, 2nd Battalion, 82nd Airborne Division, and a company commander for A Company, 2nd Battalion, 3rd Aviation Regiment. As a pilot, Rubio had over 1,100 hours of flying time, including 600 combat hours during operations in Bosnia, Iraq, and Afghanistan. Rubio received a Doctorate of Medicine from the Uniformed Services University of the Health Sciences, and completed a family medicine residency at Fort Benning. He served as a clinic supervisor and flight surgeon at Redstone Arsenal. At the time of his selection as an astronaut candidate, Rubio was the surgeon for 3rd Battalion, 10th Special Force Group at Fort Carson. In 2017, Rubio was selected as a member of NASA Astronaut Group 22, and began his two-year training.