Later, in 1980, he graduated from the University of Oslo with a Doctor of Theology degree, with a thesis on church history.
He began his career in 1958 as an assistant priest in Håland, just west of Stavanger.
Then, in 1966, he took a new job as an assistant priest in Solum, just west of Skien.
In 1983, Halvor Bergan was appointed to be the Bishop of the Diocese of Agder, based at Kristiansand Cathedral.
He held this role until the end of 1998 when he retired and moved to Melum in Skien.