Magnéli studied at Stockholm University and graduated with a Licentiate in 1941. He moved to Uppsala University to conduct his graduate research under Gunnar Hägg, obtaining his PhD in 1950 for the study on tungsten bronzes. He took up a teaching position at Stockholm University in 1953, and later became the Chair of Inorganic Chemistry at the university until his retirement in 1980.
From his research into the structures of transition metal oxides, Magnéli developed the concept of recurrent dislocations, which nowadays is known as crystallographic shear. The Magnéli phases of transition metal oxides, such as nonstoichiometric tungsten oxide, molybdenum oxide, titanium oxide, and vanadium oxide are named after him.