In 1801, he studied in Copenhagen with Wilhelm Frimann Koren Brodtkorp Christie (b 1778).
Both became "Stiftsamtmann", the King"s representative in a County. During the formation of the Constitution of Norway signed at Constitutional Assembly on the 17th of May 1814, Christie was secretary to the delegates led by Christian Magnus Falsen, and Hagerup was advisor to the Danish Prince Christian Fredrik, who was present. He was asked to accept the post of Minister, which would have required him to live in Stockholm, so he abstained.
At that time, he worked as an Assessor.
Hagerup was later appointed County Governor of Nordre Bergenhus amt (1822-1831), now named Sogn og Fjordane. Seated in Bergen, as Nordre Bergenhus was administrated from outside its territory, Hagerup was elected to the Norwegian Parliament from that city for the year 1824.
In 1827 he was elected to the Norwegian Parliament for a third time. From 1834 to 1852 he served as County Governor of Søndre Bergenhus amt (today named Hordaland).
He was a member of the first Norwegian Parliament (1814).