Telefónica Deutschland said he would leave the executive board of the company at the end of the first quarter of 2017.
Dirks came into Telefónica when the group bought German mobile operator E-Plus from KPN for €8.6 billion in 2014 and merged it with its own O2 Deutschland.
“After his decisive contribution to the successful integration and transformation of the company and on the basis of a strong company position and strategy, Thorsten Dirks wants to face new challenges in the year 2017,” Telefónica said in a statement.
He will leave at the end of March. “In the meantime, Thorsten Dirks will continue his position as CEO”, and will stay on the management board. The supervisory board is looking for a successor, it said.