French car giant PSA Group is to buy the European operations of General Motors, including Vauxhall in the UK, for £1.9 billion.
The announcement ends weeks of speculation about the deal and its impact on thousands of jobs at Vauxhall plants in Ellesmere Port and Luton.
Vauxhall employs 1,830 staff at its factory in Ellesmere Port, home of the Astra, and a further 1,530 at the plant in Luton, where they make the Vivaro van.
Unions have urged the Government to seek assurances for British workers.
Len McCluskey, general secretary of Unite, said thousands of Vauxhall workers had endured a “nerve-racking” few weeks.
“While initial discussions with the PSA Group have been relatively positive our priority now is to ensure a long-term future for our plants and the tens of thousands of workers depending on them,” he said.
Wirral Council leader Cllr Phil Davies has written to business secretary Greg Clark MP asking for an urgent meeting.
His letters asks for an assurance over Government intervention "to protect the future of the Elllesmere Port plant."
Labour MP for Ellesmere Port and Neston Justin Madders tweeted: "We have a commitment from Peugeot until 2020/21, the work starts now on protecting jobs beyond that."
Wirral South MP Alison McGovern said on Twitter: "We need certainty asap. And we need to see Government commitment to automotive production in Brexit plans.
"Working with Justin Madders & the Unite union to get clarity on future. Brexit risk shouldn't threaten automotive work."
Carlos Tavares, chairman of the managing board of PSA, said “We are proud to join forces with Opel/Vauxhall and are deeply committed to continuing to develop this great company and accelerating its turnaround.
“We respect all that Opel/Vauxhall’s talented people have achieved as well as the company’s fine brands and strong heritage. We intend to manage PSA and Opel/Vauxhall capitalising on their respective brand identities.
“Having already created together winning products for the European market, we know that Opel/Vauxhall is the right partner. We see this as a natural extension of our relationship and are eager to take it to the next level.
Mary Barra, chairman and chief executive of GM, said the deal created a new opportunity to enhance the long-term performance of the respective companies,.
He said: “For GM, this represents another major step in the ongoing work that is driving our improved performance and accelerating our momentum.
“We are reshaping our company and delivering consistent, record results for our owners through disciplined capital allocation to our higher-return investments in our core automotive business and in new technologies that are enabling us to lead the future of personal mobility.
“We believe this new chapter puts Opel and Vauxhall in an even stronger position for the long term and we look forward to our participation in the future success and strong value-creation potential of PSA through our economic interest and continued collaboration on current and exciting new projects.”
The announcement said the transaction will allow “substantial economies of scale and synergies” in purchasing, manufacturing and research and development.