It is not known if Overman, who led global brand strategy, has a job to go to. It is understood he left the company earlier this month.
A spokesman for Nokia says Overman has left to “explore opportunities” elsewhere. No decision about replacing him has been taken yet, he adds.
His departure is a blow to Nokia, which is looking to regain market share lost to Apple and Samsung and reverse a long period of declining sales.
It is said he was one of the architects of the launch campaign for its Windows 8 based range of Lumia smartphones and is thought to have been pivotal in developing much of the company’s recent global advertising and social media activity.
Overman was appointed vice president of global brand strategy and marketing creation in June 2010. Previously he led global strategy for Nokia’s ad agency Lowe Worldwide.
He also founded consultancy “The Realtime Project” in 2009, setup to advise companies on how to exploit technology.