National Grid has agreed to sell a 61% stake in Britain's £13.8 billion gas pipe network to a team of global investors including Chinese and Qatari buyers.
The deal will see a consortium led by Australian investment bank Macquarie - and including China's sovereign wealth fund - take control of the network serving 11 million homes and businesses.
UK power network operator National Grid pledged to return £4 billion to shareholders after the deal and will hand out a £150 million payment to benefit British energy customers.
It will receive £3.6 billion cash for the stake in its gas arm, as well as a further £1.8 billion in debt financing.
National Grid will retain a 39% stake in the business, but said it was also in talks with the consortium over the sale of a potential further 14% shareholding.
It comes after the Government launched a review in September of how overseas investment in UK infrastructure is scrutinised and whether ministers should have stronger powers to intervene.
National Grid chief executive John Pettigrew sought to allay fears over security of supply and said the Government and energy regulator Ofgem had been closely involved in the sale process.
He told the Press Association: "The consortium will have exactly the same obligations going forward in terms of security, reliability and safety as National Grid has had.
"It involves a group of investors who have a long track record of investing in critical infrastructure in the UK."
National Grid has around 82,000 miles (more than 130,000km) of pipeline, which delivers gas to regions including London and the East of England, the West Midlands and north-west England.
It employs nearly 5,700 staff.
Mr Pettigrew said the gas network management team will remain in place, while staff will see their terms, conditions and pension rights remain the same.
Following the deal, National Grid plans to return most of the £4 billion to shareholders through a special dividend in the second quarter of 2017.
It will also work with Ofgem to decide how best to use the £150 million payout to benefit energy customers.
The auction for the gas network has been running for just over a year and saw the Macquarie consortium fight off a raft of competitors, including a team led by Chinese investors.
For the bid, Macquarie teamed up with China Investment Corporation - a subsidiary of China's sovereign wealth fund - as well as the Qatar Investment Authority, financial services giant Allianz Capital Partners, UK-based Hermes Investment Management and British fund managers Dalmore Capital and Amber Infrastructure Limited/International Public Partnerships.
Macquarie and China Investment Corporation will hold the two largest stakes, at 14.5% and 10.5% respectively, followed by Allianz with a 10.2% stake.
The Qataris will hold an 8.5% stake.
Macquarie owns Thames Water, but is currently looking for a buyer to take on the utility giant, while others in the consortium have also invested in the Tideway Tunnel and Heathrow.
But trade union Unison claimed Macquarie was an "unsuitable" owner given its track record with Thames Water.
Unison general secretary Dave Prentis said: "Macquarie has poor form already - in building up huge company debt, repatriating massive dividends to the southern hemisphere and charging customers more for a much poorer service.
"The company has already proved it can't be trusted with the nation's water supply, but now it is to be in charge of gas pipes to millions of homes and businesses."