The firm also revealed it had struck a deal with Babcock to plan and deliver its planned new nuclear reactors.
The Horizon joint venture was set up in 2009 to build new nuclear plants to replace the 40-year old Magnox reactors at Wylfa in Anglesey and Oldbury in Gloucestershire.
But its main backers E.ON and RWE pulled out in March, which threatened to torpedo much of the UK’s ambitious nuclear power station building programme.
The pair blamed the global economic crisis and Germany’s decision to phase out nuclear power in the aftermath of the Fukushima accident in Japan for the decision to withdraw.
But this morning Hitachi announced it had bought Horizon putting plans for the two new power stations back on track.
The firm will now have to submit its advanced boiling water reactor design to UK regulators. The approval process could take up to four years, delaying the original Horizon building programme schedule.
The Japanese nuclear power station builder said it planned to make a strong commitment to the UK supply chain.
About 60% of the value of the first plant is expected to be sourced from within the UK, more for subsequent units.
Rolls Royce and Babcock International have signed a Memorandums of Understanding with Hitachi, which also today confirmed it intends to establish a module assembly facility in the UK.
Hitachi has also committed to develop a skilled workforce around the build sites.
Up to 6,000 jobs are expected to be directly supported during construction at each site, with a further 1,000 permanent jobs at each site once operational.
Under the terms of the agreement, Babcock will discuss with Hitachi and its partners, including Rolls Royce, how its skills and capabilities can be best used to support the delivery of its programme in the UK.
Peter Rogers, chief executive of Babcock said: “We are delighted to be working in partnership with Hitachi, a recognised leader in the global nuclear market.
“Our significant experience in the UK nuclear sector complements the international experience of Hitachi. We look forward to exploring how our skills, capabilities and experience can contribute to the delivery of this project of national strategic importance, meeting the future energy demands of the UK and creating long-term opportunities for UK companies.”