Professor Morrissey is a political and cultural geographer whose work draws upon the writings of Michel Foucault, Edward Said, Judith Butler and others in critiquing how dominant and violent forms of contemporary Western interventionism are underpinned by imperial and neoliberal discourses of security. His research over the last ten years has been concerned with the geopolitical scripting, political economy and biopolitics of US foreign policy in the Middle East and Central Asia, with a particular focus on United States Central Command (CENTCOM). More recently, he has begun work on the challenge of enacting more transformative and non-violent practices of 'human security' and of envisioning a 'more-than-human' sense of planetary precarity. His books include Haven (Edward Elgar Publishing), The Long War (University of Georgia Press), Spatial Justice and the Irish Crisis (Royal Irish Academy), Key Concepts in Historical Geography (Sage) and Negotiating Colonialism (Royal Geographical Society).

Professor Morrissey's research has been supported by grants from the British Academy, the British International Studies Association, the Clinton Institute for American Studies, the Irish Research Council, National University of Ireland, NUI Galway Community Knowledge Initiative, NUI Galway Millennium Fund, and the University of Cambridge. He was a Government of Ireland Fellow in 2007/08 at the Center for Place, Culture and Politics at CUNY Graduate Center, where he worked closely with David Harvey and Neil Smith. This research culminated in a geopolitical history of CENTCOM for University of Georgia Press. In 2013/14 he was elected Quatercentenary Fellow at Emmanuel College, Cambridge and Visiting Fellow at Fitzwilliam College, Cambridge. Professor Morrissey's more recent work on an IRC project, Haven, critically examined the EU's security response to the Mediterranean humanitarian crisis. As part of the project, he held visiting scholarships at LUISS University in Rome, and St Antony's College, Oxford. In 2021 Professor Morrissey was appointed International Consultant on Human Security in the Human Development Report Office of the UN. In 2023 he was elected Visiting Fellow in International Relations at Australian National University, and in 2025 he was awarded a Stokes Fellowship at the National Library of Australia for a research project exploring the political ecology writing of Judith Wright.

Professor Morrissey holds the distinction of winning the President's Award for Teaching Excellence at University of Galway on two occasions. He has also won the the NAIRTL National Academy Award for Research and Teaching Excellence. Three key areas of teaching are:

Geopolitics and War
Professor Morrissey teaches a range of modules on geopolitics, imperialism and war, focusing in particular on three wars: the Great War, the Vietnam War and the Global War on Terror.

Securitization and Interventionism
In critiquing international relations, Professor Morrissey's teaching systematically deconstructs the powerful securitization discourses underpinning forms of interventionism.

International Development
Professor Morrissey is Programme Director of the MA in Environment, Society and Development, within which he teaches modules on international development theory and practice.