Navy Lt. Cmdr. Happel attended Georgetown University, where he earned his Bachelor of Arts (B.A.) in Political Science with a concentration in political philosophy. He went on to attend Georgetown University School of Medicine and completed a transitional year of internship at the Naval Medical Center San Diego. After attending flight school, he served as a United States Naval Flight Surgeon attached to the Light Attack Helicopter Squadron 169 at Marine Corps Air Station (MCAS) Camp Pendleton, where he deployed with the Marine Medium Tilt Rotor Squadron 165 in support of Special Purpose Marine Air-Ground Task Force Crisis Response Central Command.

LCDR Happel completed his training in Internal Medicine at Walter Reed National Military Medical Center (WRNMMC), serving as chief resident thereafter. He is currently serving as the deputy service chief for the General Internal Medicine Service at WRNMMC. He is the course director for the Health Systems Science curriculum at Uniformed Services University, and remains active in Graduate Medical Education by serving as the Assistant Program Director for Quality and Patient Safety with the National Capital Consortium Internal Medicine Residency Program. LCDR Happel has been designated an American Medical Association Health Systems Scholar and is currently a Fellow at the Institute for Healthcare Improvement.