A native Texan, Dennis joined the Air Force in 1994. Becoming a Fuels Technician, he spent several tours overseas including his first permanent party assignment at Incirlik AFB, Turkey. Later he transferred to F.E. Warren AFB, Wyoming and had two subsequent deployments to Aviano AFB, Italy and Al Karj AFB, Saudi Arabia. Later transferring to Cannon AFB, New Mexico, Dennis completed his Air Force enlistment in 1999.
Following his enlistment in the Air Force, Dennis worked as an Emergency Medical Technician while completing his Bachelors of Science degree in Nursing in 2006. Following graduation he became a Commissioned Officer with the U.S. Public Health Service (USPHS). Serving with multiple agencies as USPHS officer, Dennis has worked with the Federal Bureau of Prisons, Indian Health Service, Department of Defense (U.S. Army), National Parks Service, and the Department of Veteran Affairs. Dennis completed his MBA-Healthcare Administration degree in 2016. Dennis has also worked extensively in emergency departments and in pre-hospital settings, with agencies outside of the federal government, as a Registered Nurse, Firefighter and Paramedic.