Dewar, a 31-year GM veteran, has been in charge of European sales and marketing since June 2008. Prior to that he was North American vice president of field sales, service and parts.
He began his GM career with GM of Canada in 1978 and came to the United States 10 years later as manager of strategic planning for Chevrolet. He held several field positions with the brand before GM named him executive director of sales, service and marketing in Brazil.
Two years later he returned to the United States as general manager of GMs Northeast region.
In March 2003 he became Chevrolets general marketing manager, helping launch 10 products within 20 months. He also was in charge of Chevys Chevrolet: An American Revolution ad campaign.
Dewar became North American vice president of marketing and advertising in 2005. Buick, GMC, Chevrolet and Cadillac remain part of GM following its U.S.-guided restructuring through bankruptcy. Saab, Hummer and Saturn are being sold, and Pontiac will be phased out next year.
Nesbitt, known for styling Chryslers PT Cruiser, has spent eight years at GM. Before taking the North American post in June 2007, he was executive director of design for GM Europe.
Nesbitt came to GM in 2001 from Chrysler, where he worked with Lutz. He later crafted GMs version of the PT Cruiser retro wagon, Chevrolets HHR.
Other changes in Detroit
Susan Docherty, 46, starts as general manager of the Buick and GMC brands on Aug. 1. Docherty, who currently is North America vice president for the brands, also will report to Lutz.
Jonathan Browning, 50, who is GM vice president of global sales, service and marketing, will leave the company on Oct. 1 to pursue other interests. He will not be replaced.
Douglas A. Bolduc contributed to this report