Physician, teacher, activist, diplomat, and advocate, Cahill is the director of the Institute of International Humanitarian Affairs, president of the Center for International Health and Cooperation and a University Professor at Fordham University. He serves as the director of the Tropical Disease Center at Lenox Hill Hospital, and has done extensive research and aid work in Africa, Latin America, and the Near and Far East. He is professor of International Humanitarian Affairs at the Royal College of Surgeons in Ireland, senior consultant to the United Nations Health Service, and president-general of the American-Irish Historical Society.
Cahill received degrees from Fordham University, Cornell University School of Medicine, The Royal College of Surgeons in England and The London School of Hygiene and Tropical Medicine. Upon completing his medical degree in 1961, Cahill was awarded a grant to work in Calcutta where he worked with Mother Teresa. He served as director of Clinical Tropical Medicine in Egypt and Sudan while in the U.S. Navy, and continued active medical research for the next forty years in Africa, Latin America, the Near and Far East, with long-term programs in Somalia, Sudan, India and Nicaragua.