In 1888, he was named docent of Finnish and comparative literature at University of Helsinki. In 1889, he was named acting professor of Finnish and Finnish literature and in 1898, extraordinary personal professor of Finnish and comparative folklore. In 1898, Krohn became a full professor at the University of Helsinki for Finnish and comparative folklore. Later, in 1908, when a permanent chair in Finnish and comparative folklore was established, he became its first occupant. In 1907, he created the Federation of Folklore Fellows' Communications with his friends Johannes Bolte and Axel Olrik. In 1917, he became a chairman of the Finnish Literature Society (Suomalaisen Kirjallisuuden Seura). Krohn was a co-founder of the magazines "Virittäjä" (1896) and "Finno-ugrische Forschungen" (Finno-Ugric research) together with Emil Nestor Setälä (1901). He was also famous for his 'historical-geographical' approach to comparing folklore texts.