The Japanese investors SoftBank and GungHo have bought 51.0 percent of Supercell, known for its game "Clash of Clans".
The transaction, which one source said doubled the value of Finland's game industry overnight, is aimed at exploiting synergies that can help both sides expand globally.
"This new partnership will accelerate Supercell towards our goal of being the first truly global games company," the company's chief executive Ilkka Paananen said in a statement, announcing the sale.
The objective is for Supercell to have a strong foothold both in the West and the East, including Japan, South Korea and China, he said, suggesting the company could become a new Nintendo.
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The Japanese investment provides "a massive selection of strategic resources" which will help Supercell with the distribution of its games to "hundreds of millions of new consumers all over the globe," he added.
While Supercell, a relatively new start-up from 2010, aims to expand into new Asian markets, its new investors see an opportunity to grow globally.
"In our quest to become the no. 1 mobile Internet company, we scour the globe in search of interesting opportunities and right now some of the most exciting companies and innovations are coming out of Finland," said the founder of SoftBank Masayoshi Son in a statement.
The deal follows SoftBank's move earlier this year to secure a controlling stake in number three US mobile carrier Sprint.
After "expanding its business operations from Japan to the US", SoftBank now hopes Supercell can help drive content services, it said in the statement.
The Finnish game maker is best known for its online strategy game Clash of Clans, where players build their own village and attack other villages.
The transaction will turn Supercell into a subsidiary of SoftBank through a company set up by the two Japanese investors, SoftBank said in a statement.
"Although our aspirations are global, our roots and future are very much in Finland," he said in the statement.