General Motors Co has replaced the head of its mass-market Chevrolet brand as the management shake-up continues at the top U.S. automaker.

Brent Dewar, a 31-year GM veteran, will retire in April 2010 and serve out the remainder of his career as an adviser to the newly appointed head of North American operations, Mark Reuss.

Dewar, who had introduced fuel-efficient GM models at last week's Los Angeles auto show, will be replaced immediately as head of Chevrolet by James Campbell, a 45-year-old executive who had previously headed Chevrolet's fleet sales operations.

The change comes at a time of tumult in GM's executive ranks as executives who devoted a full career to the Detroit-based automaker find themselves being shown the door.

The Chevrolet appointment is especially crucial because GM expects the brand to carry the burden of driving sales and market share as it sheds Hummer, Saab, Saturn and Pontiac.

Dewar, who previously headed GM sales in Europe, had been appointed to lead Chevrolet in July as the automaker emerged from bankruptcy after taking $50 billion in government aid.

Dewar had been appointed by former GM Chief Executive Fritz Henderson, who resigned last week in a split with the automaker's board led by Ed Whitacre.

The Obama administration dismissed Henderson's predecessor, Rick Wagoner, in March after he resisted calls to consider a restructuring in bankruptcy.

Henderson had vowed to shake up GM's insular and slow-moving decision-making process, but resigned after eight months on the job when the automaker's board decided to push for faster changes under new leadership.

GM Chairman Whitacre, who also became acting chief executive with Henderson's departure, said this week that the new team of GM executives would not have long to show results.

The automaker is on the verge of hiring a new chief financial officer, Whitacre said this week.

(Reporting by Kevin Krolicki, editing by Leslie Gevirtz)

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