Dr Fleming is a Senior Lecturer in History and a historian of eighteenth-century Ireland. On completing his undergraduate studies at the University of Limerick, he was awarded, in 2006, a DPhil from the University of Oxford, where he had been a senior scholar at Hertford College and an Arts and Humanities Research Council postgraduate awardee.

His research concentrates on the social and political development of eighteenth-century Ireland, and has published on topics ranging from provincial politics, poverty, religious conversion, associational behaviour and prostitution. Dr Fleming was commissioned, in 2012, to write the official history of the University of Limerick.

Dr Fleming teaches courses on 'Early Modern Ireland' and delivers a specialist module to advanced history students: 'Conservatives, patriots and radicals: politics and political ideology in eighteenth-century Britain and Ireland'. 

In 2006, he was a Price Fellow at the William L. Clements Library, University of Michigan, where he catalogued the extensive papers of General Sir Eyre Coote (1762-1823). A year later he was an Irish Research Council for the Humanities and Social Sciences Postdoctoral Fellow. In 2015-16, Dr Fleming was a Fulbright Scholar at the University of Montana, where he delivered modules in Irish history as part of that University's Irish Studies programme.

Dr Fleming is treasurer of the Group for the Study of Irish Historic Settlement, an interdisciplinary forum for historians, geographers, archaeologists and others interested in settlement history in Ireland. He was secretary of the Eighteenth-Century Ireland Society for many years. Between 2013 and 2017, he was chairman of the Irish Georgian Foundation, and a trustee of the Hunt Museums' Trust.