The plan includes measures to reduce salaries by €265 million per year, Opel said.
"This European framework contract and the specific agreements in each country, including Germany, are important steps along the way to a new and successful company," Opel chief executive Nick Reilly told a press conference.
He spoke alongside Klaus Franz, head of GM Europe's works committee.
Opel workers agreed to the salary reductions as part of a plan that includes 8,300 job cuts from a total of nearly 50,000 in Europe.
A formal signing of the accord was expected in the coming days, Reilly said.
It includes the transformation of Opel's corporate statutes so staff can eventually share in company profits.
In all, GM expects to invest €1.9 billion in its restructuring of Opel, and has asked European countries where its plants are located to contribute €1.8 billion in public guarantees.
GM has run into stiff opposition to its plan in Germany however, which has been asked to provide more than €1 billion, and where 3,900 jobs are due to be eliminated.