Friesen began teaching in Nordic Languages at Uppsala University in 1897 and finished his dissertation there in 1898. He became a Professor of Swedish in 1906.
Published works include Om de germanska mediageminatorna (1897), Till den nordiska språkhistorien (1901 and 1906), as well as Om runskriftens härkomst (1904–06), Vår äldsta handskrift på fornsvänska (1906) and "Kylverstenen" (in Antiqv. tidskrift, vol. XVIII).