Activity on the Wylfa Newydd project was suspended in 2019 after funding negotiations with the Government hit an impasse.
Hitachi is expected to formally drop the scheme at a board meeting today but has written to Isle of Anglesey council confirming its is walking away from the project.
The project was expected to receive a development consent order at the end of this month and would have sustained 9,000 jobs bringing a big economic boost to North wales.
The decision sent a shockwave through the nuclear engineering industry.
Firms bringing forward the Sizewell C, many which were also involved with Wylfa, said it was now essential that Sizewell C advanced to construction to protect the nuclear engineering supply chain.
Cameron Gilmour, spokesperson for The Sizewell C Consortium, said: “This news will have serious ramifications for companies both in Wales and across the UK.
“The Wylfa nuclear project would have been another important milestone for the UK’s nuclear supply chain and would have created thousands of jobs.
“Unless Sizewell C, a replica of the under-construction Hinkley Point C, is given the go-ahead, there is now a serious risk to the future of the UK’s civil nuclear construction capability and the tens of thousands of jobs that go with it.”