He was elected to the Norwegian Parliament from the Market towns of Hedmark and Oppland counties in 1950, and was re-elected on two occasions. Midway in his third term, he died and was replaced by Trygve Owren. Outside politics, he worked as a wholesaler.
Granum was a member of Gjøvik city council in the periods 1945–1947 and 1955–1958. He was a member of the national party board from 1950 to 1954.