Born in Belfast, Northern Ireland, Mackie holds degrees from McGill University, Cornell University, and Michigan State University. She originally began her professional career as an agricultural economist in Nigeria for Stanford University, but the Biafran War forced her return to the United States. At that point, she became a member of the Washington University School of Medicine faculty. At Washington University, Mackie acted as a liason between the medical center and the division of Health Care Research. In the early 1970s, she was called back to Africa and spent the next two decades working with USAID and the Foreign Service in Chad. In her retirement years, Mackie has lived in Zimbabwe, South Africa, and the U.S.