He formerly worked as a clinical instructor at the University of California, San Francisco, Department of Family and Community Medicine. His volunteer efforts include stints as a volunteer physician at Albert Schweitzer Hospital, Haiti; at Guayaquil Infectious Diseases Hospitals, Ecuador; and and as a volunteer coordinator at the Center for AIDS Services. His primary areas of interest include informing the California health care agenda, the state's immigration debate, and work for those living with HIV and AIDS. Dr. Halligan received his medical degree from Loyola University, Chicago, Stritch School of Medicine in 1998 and completed his residency in family medicine as Chief Resident at University of California, Los Angeles, Ventura County Medical Center in 2001.