The Unite workers union says it has reached a deal with Magna, the proposed new owners of Vauxhall, to protect jobs at Ellesmere Port and Luton.
Unite says that, following the deal, about 600 jobs will go, all through voluntary redundancy. It had been feared that 1200 of the 5,000 Vauxhall jobs in the UK could be cut.
Unite says it has agreed to a two-year pay freeze and other cost-savings in return for having no compulsory redundancies. It also said that there would be an increase in working hours to top up workers' earnings over the next two years.
Tony Woodley, joint general secretary of Unite, said the deal: "gives both plants job security and a future through to 2013, providing a good basis for a long-term future beyond that."
A Vauxhall statement said: "This is very good news for Vauxhall's UK operations and is the result of a tremendous team effort between [the] leadership of Unite and the management team at Vauxhall."
Magna declined to comment on the union's announcement.
The business secretary Lord Mandelson said there was still "some way to go" in agreeing the financing of the deal.