In 1899 he published his thesis Studier over de norske byers selvstyre og handel før Hanseaternes tid ("Studies Concerning the Norwegian Cities' Autonomy and Trade Before the Time of the Hanseatic League"), and obtained his dr.philos.
[1] Bugge won an essay competition sponsored by the Nansen Foundation in 1903 on the question "How or to which extend have the Norse, and particularly the Norwegians, culture, way of living and society been influenced from the Western Countries [i.e. the British Isles]".
He published numerous scientific articles, his main sources being the early development of Norwegian cities and trade as well the cultural relations in the time of the Vikings.
He also edited and translated into English the complex Irish tract Caithréim Chellacháin Chaisil (The Victorious Career of Cellachán of Cashel), published in 1905.
According to Halvdan Koht, "being a teacher cost him [Bugge] unspeakable hardships... ...in the end making him sick"[note 1][2] According to Claus Krag, he also in suffered periods of serious problems related to alcohol.