He graduated as mag. art. in Public Administration and Organizational Theory from the University of Bergen in 1971. He worked as a researcher at the Norwegian State College of Local Government Administration and Social Work from 1971 to 1978, and associate professor from 1992 to 1994. When the Oslo University College was established in 1994, Stjernø became the rector there, a position he held until 2000. Since 2002 he is professor of social policy and social work. He has been a visiting scholar at the University of Bremen, the University of New South Wales and the University of California, Berkeley.