Seppo Harjanne (born 28 February 1948) is a Finnish retired rally co-driver. He is best known for co-driving for Timo Salonen from 1979 to 1988 and for Tommi Mäkinen from 1990 to 1997. With Salonen, Harjanne took ten World Rally Championship victories for the factory teams of Datsun, Peugeot and Mazda, and the 1985 drivers' world championship title in a Peugeot 205 Turbo 16 E2. With Mäkinen, competing mainly for the Team Mitsubishi Ralliart, he won ten more WRC events along with the 1996 and 1997 drivers' titles in a Lancer Evolution.

Harjanne retired after the 1997 season and Mäkinen went on to take two more titles with Risto Mannisenmäki. Since retiring he has worked as a Deputy Clerk of the Course of Rally Finland since 2000 and assisted in organising several other international rallies.