Hempton was born on 19 February 1952, in Northern Ireland. He earned his B.A. (1974) from the Queen's University Belfast and his Ph.D. (1977) from the University of St Andrews. Hempton began teaching at Queen's University in 1979, where he was professor of modern history and director of the school of history. He joined the faculty of Boston University in 1998, where he was professor of the history of Christianity, and in 2008 named "Outstanding Teacher of the Year" at the divinity school. In 2007, he was appointed as the first Alonzo L. McDonald Family Professor of Evangelical Theological Studies at Harvard Divinity School, and in 2012 it was announced he would succeed William A. Graham as dean of the school.