He then moved to Ireland to do PhD work at Trinity College, Dublin. His thesis was on the Irish Republican Army in County Cork, an epicenter of the Irish War of Independence, which was the basis of his first book, "The IRA and its Enemies". After completing his doctorate, Hart accepted a five-year teaching and research position at Queen's University Belfast. In 2003, having completed this contract, Hart moved back to Canada to take up the position of Canada Research Chair in Irish Studies at the Memorial University of Newfoundland. He was also an associate professor at Memorial University.