A Chevrolet spokesman confirmed that Smettem left the company in April and that managing director Andy Carroll and GM were reviewing the future of the marque's marketing department.
GM has already assimilated Saab's marketing function into Vauxhall. However, integrating Chevrolet would not be as straightforward, because 48% of Chevrolet's holding company, GM Daewoo Auto, is owned by banks and creditors, whereas Saab is wholly owned by GM.
A spokesman at Chevrolet said that during the review Carroll has assumed responsibility for the marketing function.
Smettem joined Chevrolet in 2003 after leaving Jaguar, where he was global marketing communications manager, running its Formula One sponsorship.
He was responsible for the 2004 rebrand of Daewoo to Chevrolet and handled the launch of the Matiz model in 2005. He also oversaw the Matiz sponsorship of ITV show Celebrity Love Island.
General Motors bought South Korean marque Daewoo shortly after it sought bankruptcy protection in 2002. Its cars are branded as Chevrolet in all markets outside of South Korea.
Chevrolet's decision to review its marketing structure comes ahead of the £40m pan-European launch of the Captiva SUV.
Insiders consider the model to be its most important marketing challenge since the Daewoo rebrand, as it comes closest to what the European market believes a Chevrolet should look like. The launch campaign is being handled by FCB London.
Chevrolet sold about 15,000 cars last year, according to the Society of Motor Manufacturers and Traders.