Dr O'Sullivan's primary research interests lie in the area of family law and property law. She has conducted considerable comparative research analysing the family property schemes which apply in a number of jurisdictions while a relationship continues, on death and on relationship breakdown. In more recent times, she has also explored broader issues in family law (marriage/wedding laws), property law (drones and ownership of airspace) and within religious law. 

Kathryn has a keen interest in teaching and learning. She completed a Specialist Diploma in Teaching, Learning and Scholarship in 2014, graduating with First Class Honours, and was recognised with the University's 'Excellence in Teaching Award 2018' having previously received a Special Commendation for Excellence in Teaching in 2015. She has secured national funding from the National Forum for the Enhancement of Teaching and Learning in Higher Education on two occasions. 

Professor Kathryn O'Sullivan is a lecturer at the School of Law, University of Limerick, Ireland. Kathryn's primary research interest lies in the laws governing family property and finances. She has published widely in highly respected national and international journals (including Legal Studies, the International Journal of Law, Policy and the Family and the Journal of Social Welfare and Family Law) and has provided expert analysis of legal issues for national media outlets including RTÉ Radio 1 and the Irish Times. In terms of impact, she was invited in 2022 to provide expert evidence to the Women and Equalities Committee of the UK Parliament on the issue of cohabitants rights while her work has also been cited by the United Nations, the Norweigan Department of Investigations, the British Columbia Court of Appeal in Canada, the Irish High Court and the Law Reform Commission of Ireland. She is the Corresponding Member for Ireland with the Cambridge Family Law Centre at the University of Cambridge and was selected as a Dobbin Atlantic Scholar for 2017/18 by the Ireland Canada University Foundation.