Dohler had been with Vattenfall since 1998 and had served as CFO since December 2016.
He will temporarily remain in his position "to ensure a smooth transition of his areas of responsibility", Vattenfall said. He is due to start in the new role by 1 April 2018 at the latest. Vattenfall is searching for a successor.
"After such a long time in the company, such a decision is, of course, accompanied by mixed feelings," Dohler said.
"Vattenfall has shaped my professional career and provided me with extraordinary development opportunities, and I have enjoyed working with so many great colleagues."
EWE is part of the consortium developing the 203MW Trianel Windpark Borkum II (TWB II) offshore wind site in the North Sea, which reached a final investment decision in May 2017.
It also owns stakes in the 113MW Riffgat and 62MW Alpha Ventus offshore wind projects in Germany as well as an onshore wind portfolio.