Hermes, 39, replaces Thomas Schweisfurth who left the Dortmund-headquartered pump manufacturer last year.
Hermes has been responsible for the Wilo's Finance, Control and Human Resources functions at board level since October 2006. As the chairman of the executive board, Hermes will take on the additional tasks of strategy development as well as internal and external communications.
Before joining Wilo, Hermes was a partner with the audit firm KPMG.
Wilo manufactures pumps and pump systems for heating, cooling and air-conditioning technology and for water supply and drainage and sewage. The company has representative offices in more than 70 countries and employs approximately 6000 people worldwide. The company had a turnover of €977 million in 2008.