Karlsen is a political scientist with a PhD from the University of Oslo (2009), and has been at the Institute for Social Research since 2013 (Research Professor since 2014). He was a Postdoctoral Fellow at the Department of Political Science, University of Oslo (2009-2013), and a Research Fellow at the Institute for Social Research (2005-2009).
His research interests include political communication, campaigns, elections, new media technology, political parties and political representation.
Karlsen currently leads to projects both financed by the Research Council of Norway:
Disruptive Change and New Media Policies: A Field Approach
Growth, Integration, and Coordination in Executive Government
Karlsen has been a key member of the Norwegian Election Studies since 2005, and is the editor of "Tidsskrift for samfunnsforskning" (Journal of Social Science), the leading social science journal in Norway.