In addition to professional work, he has since the late 1960s contributed actively to public debate on a variety of issues. Slagstad was editor of Pax Publishing (1971–1978) and the Norwegian University Press (1986–1989). He has held tenured professorships both at the University of Oslo, the Norwegian Institute for Social Research and Oslo University College and headed The Research Council of Norway Program on Governance and Democracy ("LOS") (1990–1998).
He initiated and co-edited the encyclopedia PaxLeksikon (with ia Hans Fredrik Dahl and Jon Elster), co-edited the leftist journal Kontrast, and was editor-in-chief of the intellectual journal Nytt Norsk Tidsskrift from 1984 through 2009.
From 2009-2013 Slagstad held a professorship at the Centre for the Study of Professions at Oslo University College. He is currently at The Institute for Social Research working on a study of Scandinavian social-democratic sittlichkeit.
He has three children. He was in 2005 announced Norway’s leading intellectual by the daily newspaper Dagbladet.
In 2006 he played flute in the church service for Jens Chr Hauge—a rendition of traditional folk tune "Jeg lagde mig saa sildig".