Fields has conducted national-level research within the HIV Vaccine Trials Network (HVTN) and the HIV Prevention Trials Network(HPTN). Along with these endeavors, Fields began his career as an assistant professor at Binghamton University from 2000 to 2001. While in Rochester, New York, in 2009, he was selected for the highly competitive and prestigious Robert Wood Johnson Health Policy Fellowship, which allowed him to work in the office of United States Senator Barbara Mikulski (D-MD).