Hitachi will buy Horizon Nuclear Power, which is set to build new reactors on existing sites in Anglesey in Wales and at Oldbury near Bristol, the BBC reported Tuesday.
Hitachi said it will buy Horizon from German companies E.On and RWE, which are withdrawing from the U.K. nuclear market.
RWE and E.On put Horizon up for sale in March following Germany's decision to move away from nuclear power following Japan's Fukushima disaster.
British Prime Minister David Cameron said Hitachi's commitment is a major development.
"This is a decades-long, multibillion-pound vote of confidence in the United Kingdom that will contribute vital new infrastructure to power our economy.
"It will support up to 12,000 jobs during construction and thousands more permanent highly skilled roles once the new power plants are operational, as well as stimulating exciting new industrial investments in the U.K.'s nuclear supply chain," he said. "I warmly welcome Hitachi as a major new player in the United Kingdom energy sector."
Hitachi said it intends to build 6 gigawatts of nuclear capacity, with the first plant coming online in the first half of the next decade, once its reactor design is approved by the necessary authorities.