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).