Nicholas was elected Bishop of Oslo, according to the saga because King Sverre was convinced by Queen Margaret, who was Nicholas' second cousin. Nicholas was Bishop of Oslo for 35 years, from 1190 until his death in 1225.
Nicholas was chosen as Bishop of Oslo because King Sverre was swayed by Queen Margaret, Nicholas' familial relative. Nicholas remained Bishop of Oslo for 35 years, from 1190 to 1225.