Riksantikvaren
He was educated as an architect at the Norwegian Institute of Technology from 1969 to 1974, and was hired at the Norwegian Directorate for Cultural Heritage in 1979. In 1991 he was promoted to head of the technical department. In 1995 he was promoted to acting director of the organization, meant to replace Øivind Lunde in the last two years of Lunde's designated six-year term. Marstein was the first architect in 82 years to head the Norwegian Directorate for Cultural Heritage.