Magnús is a medical doctor who graduated from University of Iceland and trained in internal medicine and infectious diseases at Duke University Medical Center, Durham, North-Carolina, USA.
He has worked as consultant in clinical infectious diseases for more than 20 years at Landspitali University Hospital in Reykjavik, Iceland and as professor at the University of Iceland from 2008. Fulbright scholar at the National Institutes of Health, US in 2010-2011.
He has supervised numerous graduate students and worked as a consultant for the WHO/Global Fund on HIV.
Magnús is the past president of the Nordic Society for Clinical Microbiology and Infectious Diseases (NSCMID) and editor in chief of Laeknabladid, The Icelandic Medical Journal.