The GIB said the investors included UK pension funds and a sovereign wealth fund. The GIB has also added £200 million to the fund, which has an expected life of 25 years.
Additionally, the GIB has transferred its assets in the 90MW Rhyl Flats and 317MW Sheringham Shoal projects to the fund. It owns 24.95% and 20% of these projects respectively.
A new FCA-regulated division within the GIB will manage the fund.
However, the iniative is still short of its original aim to bring £1 billion of investment when it announced the plan last year.
Speaking about the fund, GIB chief executive Shaun Kingsbury said: "The fund will create significant benefits for the UK by mobilising capital into the UK offshore wind sector from new, long-term investors seeking good, risk adjusted returns.
"Attracting additional capital and creating a liquid market for operating assets is an important step in reducing the cost of offshore wind and supporting the continued growth of the sector. New investors will allow the original developers to sell down their stakes and use the proceeds to finance new renewable energy projects."
The UK government officially launched the GIB in 2012 with £3 billion (€3.7 billion) in funding.
The aim of the bank is to fund finance low-carbon developments, with offshore wind energy a priority. The bank's remit was also to encourage private-sector investment.