The government will also be appointing independent trustees with the power to ensure the GIB continues to have an "environmental mission".
It will establish three new investment vehicles - an offshore wind investment vehicle, a low carbon lending platform and a green infrastructure investment platform.
But the Government said today that under Macquarie's leadership the GIB "will invest more into the green economy than ever before". "The GIB has been very successful in attracting private capital to the UK's green economy".
Liberal Democrat Ed Davey, formerly United Kingdom energy and climate change secretary, described the deal as "politically dubious" and tantamount to "selling off the family silver".
'GIB has a well-funded new owner committed to the bank's green mission'. The Green Purposes Company Ltd (GPC) which holds the special share, sought to downplay fears of a change in goal of the bank in its response to the news. This will include publishing an annual report on its green performance, holding an annual industry day for stakeholders and green reporting.
Ed Davey, former energy secretary, said: 'Selling the GIB is environmentally irresponsible and, on the eve of an election, is politically dubious'.
In a written statement this morning, he said the bank's green objective would be maintained, with Macquarie publishing a series of commitments over the GIB's future.
The Green Investment Bank will build on an unrivalled track record of investing in United Kingdom green infrastructure.
There had been fears that Macquarie would asset-strip the bank, leading to speculation a sale could be scrapped in favour of a flotation. This has included around £1.5 billion in backing from the government itself, as well as further investment from private sector partners. Macquarie is now also advising on 850MW of tidal projects under development.
"There is a compelling logic in the world's first green bank joining forces with the world's largest infrastructure investor", he said in a statement. More broadly, Macquarie has led over £35 billion of investment in United Kingdom infrastructure, including the National Grid gas distribution networks, the Mersey Gateway Bridge and the Edinburgh Hospital for Sick Children.
Climate change minister Nick Hurd says all taxpayer funding invested has been returned with "substantial profit". Macquarie is committed to UKCI and its vision to invest internationally.
It is an important move given Macquarie is the biggest infrastructure investor globally, while USS is one of the UK's largest pension funds with around £57bn in assets under management.
Since it was set up it supported more than 100 renewable and low-carbon projects across the United Kingdom and raised £3 of third party capital for every £1 it invested. Investors in the fund include United Kingdom local authority pension schemes such as Strathclyde Pension Fund, Swedish life insurance and pension company AMF, and a Middle Eastern sovereign wealth fund.
Mike Powell, head of private markets at the USS, said: "This transaction has enabled USS to acquire a portfolio of high quality renewable energy assets on behalf of our members". It has backed projects from wind farms to biogas plants. "Our combined platform will build on the legacy of the GIB and, alongside our knowledge of energy and infrastructure, will open further opportunities in low carbon investment both in the United Kingdom and further afield".
It pledged to strengthen its commitment to Scotland by providing new opportunities for the low-carbon and financial sectors. The sale proceeds will be received on completion of the transaction, which the government expects to take around two months.