Professor Celius has a medical degree from the University of Bonn, Germany, and was certified in neurology in 1993. She has worked as a consultant with a special focus in MS at the Oslo University Hospital since 1987, acting as Head of the Neurological Department from 2002 to 2010 and Group Leader of the MS research group since September 2018. Professor Celius is a member of the reference group preparing guidelines for treatment of MS in the Norwegian Directorate of Health, as well as being a member of the European Committee for Treatment and Research in MS (ECTRIMS).

Professor Celius has a special interest in MS epidemiology and clinical studies, but also participates in genetic and gene-environment studies. She regularly takes part in the development of local, national and international data collections and research projects.