Together, the firms are developing the 33MW Ohorayama project in the Kochi prefecture of Japan's southern Shikoku Island.
The project has signed a 20-year power off-take agreement with local utility Shikoku Electric Power. Construction is due for completion by March 2018.
"We are making steady progress on our commitment to develop 1GW of new renewable energy sources in Japan, demonstrating the value of our partnership with GPI," said Pattern CEO Mike Garland.
It is the developers' first wind project to reach financial close, following the completion of two solar projects in 2016.
"This achievement is a reflection of the effectiveness of our partnership, and we are excited about further executing on our portfolio of mature development assets. We expect our next project, a 126MW wind farm in Aomori prefecture, to reach financial close and commence construction by mid-2017. It is anticipated to be the largest wind project in Japan," said GPI chief executive Toshio Hori.
Pattern and GPI formed the partnership in January 2015, when the US firm acquired a majority stake in the Japanese developer.