Mr Tsurunen wants more foreigners in Japan's politics
Mr Tsurunen, who became a Japanese citizen more than 20 years ago, is already well-known for his work as a local politician and writer.
Japan is very homogeneous and only 1.5% of the population are foreign-born.
Career change
Mr Tsurunen, 61, came to Japan as Martti Turnen in 1967 as a missionary.
He married a Japanese woman and took Japanese citizenship in 1979. He is the author of two books, "I want to be Japanese," and "Here comes a Blue-Eyed Assemblyman."
He has already made history in Japan - becoming the first foreigner to enter his local assembly 10 years ago.
The Finn made four unsuccessful bids to win a seat in parliament for the opposition Democratic Party of Japan (DPJ) before becoming the default choice to replace television celebrity turned MP Kyosen Ohashi.
He resigned last week complaining of conflicts with his party leadership.
Mr Tsurunen has said that he wants to increase the number of foreign faces in Japanese politics.
Hostility
"Some people are expecting miracles from me. They say 'please change Japanese politics'. I say I can't do it alone. It's the voters that can do it," he told Reuters news agency.
The former English teacher says most Japanese seem to have finally accepted the idea of a foreign politician, although he has met hostility and even racism.
"Some right-wing groups were threatening me, giving me phone calls saying go back to Finland, saying we don't need foreigners in our assembly," he said. "There was also blackmailing. Telling lies about me or my background... But no one killed me, so I am still here."
Pressure is growing on rapidly greying Japan to rejuvenate its work force. According to a report by the United Nations it will need to import around 600,000 workers annually until 2050 to keep its working population afloat.