Professor Mortensen's research and publication is in the fields of lawyers' ethics and international and comparative law. In lawyers' ethics, his work centres on philosophies of virtue, and his writings have addressed their relationship with moral and legal theories of care, religious perspectives on legal practice, lawyers' character, the reform of the legal profession in Queensland and the management of client money. Professor Mortensen's work in international and comparative law concentrates on private international law. With Richard Garnett and Mary Keyes, he is the author of the standard Australian text in this field, Private International Law in Australia (2nd ed, LexisNexis, 2011), and has published research on international jurisdiction, the transnational enforcement of judgments and choice of law. A particular focus of Professor Mortensen's research is the use of private international law in trans-Tasman economic integration. Work in choice of tort law and renvoi has appeared in the Journal of Private International Law and the International and Comparative Law Quarterly.