He has appeared in over 40 films and TV series. Of these, the most famous are A Summer by the River, Ambush, Mustan kissan kuja, Badding, On the Road to Emmaus, Rölli ja metsänhenki, Kuutamolla, Bad Boys, Dog Nail Clipper, Matti, Hellsinki and Kerron sinulle kaiken. For his role in Dog Nail Clipper, Franzén was awarded a Jussi Award for Best Actor as well as earning praise from film critic Jay Weissberg from Variety magazine who called the actor "one of the most talented and versatile thesps in Finland".
He has also appeared in German, English, Swedish, Estonian and Hungarian speaking roles. Franzén had a role as a Russian corpse in one episode of CSI: Miami, and more recently was cast for a small part as a police officer in the movie Cleaner by Renny Harlin. In 2009, Franzén had a small role as a Swedish Viking in the True Blood episode Never Let Me Go.
- Peter Franzén and Jasper Pääkkönen played brothers previously in the FInnish movie "Heart of a Lion". According to the actors, this put them on the radar of the casting directors of Vikings.
- He played opposite Alexander Skarsgård, Gustaf Skarsgård's brother, in True Blood.