Slaughter is a 1976 graduate of St. Anne's-Belfield School in Charlottesville, Virginia. She graduated magna cum laude with an A.B. from the Woodrow Wilson School of Public and International Affairs at Princeton University in 1980, where she also received a certificate in European Cultural Studies. Mentored by Richard H. Ullman, she won the Daniel M. Sachs Memorial Scholarship which provides for two years of study at Worcester College, Oxford. After receiving her M.Phil. in International Affairs from Oxford in 1982, she studied at Harvard Law School and graduated "cum laude" with a J.D. in 1985. She continued at Harvard after graduation as a researcher for her academic mentor, the international lawyer Abram Chayes. In 1992, she received her D.Phil. in International Relations from Oxford.