Fritz Henderson has resigned from his role as chief executive of General Motors.
GM's chairman of the board, Ed Whitacre Jr, will serve as an interim replacement.
Whitacre is understood to want to ramp up the pace of change at GM. A former telecoms executive, he was brought in as GM's chairman in June by the Obama administration, and admitted at the time: "I don't know anything about cars".
The unexpected news of Henderson's departure, "by mutual consent", came minutes after the end of a GM board meeting to discuss the fate of its Swedish car brand Saab.
GM said that due to the emergence of new potential buyers it would evaluate bids for carmaker Saab by the end of December.
GM said that if it did not find a "suitable arrangement" it would then "wind down" Saab.
About 4,500 jobs at Saab are at stake.
New chief executive
Whitacre commended what he described as Henderson's "remarkable job in leading the company through an unprecedented period of challenge and change".
"While momentum has been building over the past several months, all involved agree that changes needed to be made," the statement continued.
The White House denied any involvement in the resignation.
"This decision was made by the Board of Directors alone. The administration was not involved in the decision," a White House spokeswoman said.
In March, Henderson replaced the then chief executive, Rick Wagoner, who was ordered to step down by US President Barack Obama.
Wagoner had headed the company since 2000, after first joining the company in 1977.