GM said last week that the group’s Russelsheim plant had won a crucial contract to build the vehicle in a fight to secure thousands of jobs.
It pitted the German plant against Saab’s factory in Trollhattan, Sweden.
Saab chief executive and chairman Peter Augustsson, with the firm since 1998 as deputy head and then head, has decided to leave the group as of April 1, GM said in a statement.
GM Europe President Carl-Peter Forster will replace Augustsson as Saab chairman, while Jan-Ake Jonsson will assume the role of managing director of the brand.
"I felt that it was the right time for me to move on to something I’ve wanted to do for some time," Augustsson said. He plans to start a business development company.