The company said Obermann, whose contract had been due to run until end-October 2016, had asked the supervisory board to release him from his duties from end-December next year and it had approved the request.
Obermann said in a statement that he wished to get more involved in daily operations again.
"I want more time for customers, product development, and techology," he said.
He has held the top job at Telekom since 2006.
Replacing him will be finance chief Timotheus Höttges, who will assume the CEO job in January 2014, and from next month become deputy CEO in addition to his current duties, a company statement said.