Dr. Midtvedt studied medicine at the University of Oslo, Norway (1952-1956) and the University of Bergen, Norway (1956-1958). He received his license to practice medicine from the Norwegian Board of Health in 1959. He earned his Ph.D. degree (Doctor of Medicine) at the Karolinska Institute, Sweden, in 1968. In 2010 he was promoted to Doctor of Veterinary Medicine Honoris Causa by the Faculty of Veterinary Medicine of the Norwegian University of Life Sciences.

Dr. Midtvedt held different positions at the Faculty of Medicine of the University of Oslo until he was appointed Professor of Medical Microbiology in 1982. In 1983 he was appointed Professor and Chairman of the Department of Medical Microbial Ecology, Cell and Molecular Biology at the Karolinska Institute in Stockholm, Sweden. He held this position until his retirement in 1999.

Dr. Midtvedt is a member of several national and international organisations, is Editor-in-Chief of the journal ‘Microbial Ecology in Health and Disease’ and member of the Editorial Board of 3 international journals. He published more than 880 publications on antibiotics, ecology, gnotobiology, infectious diseases, microbiology, and pharmacology. He is still involved in a number of research projects.