The Green Investment Bank Offshore Wind Fund will be managed by a subsidiary of the GIB, following approval from the UK regulator, the Financial Conduct Authority.
In March, GIB announced it would spend £220 million (EUR 266 million) on a 10% stake in the 576MW Gwynt y Môr project off the UK's northwest coast.
The announcement comes as the GIB released its results for the 2013/14 financial year - ending 31 March 2014.
Results show the GIB invested £668 million (EUR 833 million) across 18 green energy initiatives over the 12-month period.
However, the bank posted an operational loss of £5.7 million (EUR 7.2 million) in the financial year, in line with expectations, because most of its investments are in the construction phase. Profits should come in future years once the projects begin operation.
Since the bank was set up 18 months ago, it has invested £1.3 billion (EUR 1.6 billion) in the renewable energy sector.