Finn Kristian Marthinsen (born 17 January 1946 in Brunlanes) is a Norwegian politician for the Christian Democratic Party.
He was elected to the Norwegian Parliament from Buskerud in 1997, and was re-elected on one occasion.
Marthinsen was a member of Drammen municipality council from 1999 to 2003.
He took the initiative to revive the pro-Israel parliamentary caucus Friends of Israel in the Parliament of Norway in 2002, of which he became chairman.