In 1811 he entered the University of Lund, where he in 1814 he was appinted associate professor of botany and in 1824 full professor. In 1834 he became professor of practical economy at Uppsala University. On the death of Göran Wahlenberg (1780-1851) he was appointed professor of botany at Uppsala.
Fries is, after Persoon, considered to be founding father of modern mushroom taxonomy (see mycology). His taxonomy of mushrooms was influenced by German romantics (see Goethe). He used spore color and arrangement of the hymenophore (pores, gills, teeth etc.) as major taxonomic characters.
See also: List of Swedish scientists