Whitacre, 68, who has served just eight months as chief executive of the top US automaker, said he would resign on Sept. 1, to be replaced by Dan Akerson.

Akerson, 61, was named to GM's board by the Obama administration a year ago when the automaker was restructured in bankruptcy with $50 billion of US government funding.

A veteran deal maker and a managing director The Carlyle Group for the past seven years, Akerson spearheaded some of the private equity firm's biggest recent deals including the buyout of energy company Kinder Morgan.

Whitacre's departure had been expected, but the timing of his announcement caught even GM insiders off guard, just a day ahead of GM's expected filing for a landmark stock offering.

Whitacre, who continued to commute from his home in Texas during his stint as CEO of the Detroit-based company, had said repeatedly that he would be an interim leader.

"It was obvious that I was not going to be at GM for the long haul," Whitacre said at the end of a conference call to discuss the company's second-quarter earnings.

"We have put a strong foundation in place, so I am very comfortable with my timing."

Akerson, also a former CEO at Nextel, will become GM's fourth chief executive in just a year and a half, underscoring the challenge in remaking the corporate culture of an automaker still in the early stages of a turnaround.

GM posted a second-quarter profit of $1.3 billion in evidence of a turnaround driven by cost-cutting in its 2009 bankruptcy and better sales in the United States.

The second-quarter profit was the largest since 2004, when the US auto market was still booming with annual sales of near 17 million vehicles and GM's brands accounted for more than one in four purchases of new cars and trucks.

The results reflected a 47 percent snap back in global production from the depressed levels of a year earlier when GM began operating under bankruptcy.

Revenue rose to $33.2 billion from $31.5 billion in the first quarter, boosted by higher sales of more profitable new models such as the Chevrolet Equinox.

Europe, where GM is still struggling to restructure its Opel unit, remained a notable weak link for the automaker with an operating loss of $160 million.

North America had an operating profit of $1.6 billion. International operations, including GM's China joint ventures with SAIC and Wuling, had an operating profit of $672 million.

GM lost about $88 billion between 2005 and 2009 when it was driven into bankruptcy by plunging sales and tight credit.

The last time the automaker had consecutive quarters of profits was in 2004, when it had a 26-percent share in a US auto market that was near record-high levels.