From 1977, he worked for the company’s power generation subsidiary Kraftwerk Union AG (KWU).

In 1989, he became President of KWU and a member of the Managing Board of Siemens AG.

In 1992, Pierer succeeded Karlheinz Kaske as CEO and held this post until January 2005, when Klaus Kleinfeld took over.

He also functioned as an advisor to the German governments under Gerhard Schröder and Angela Merkel.

In April 2004, Pierer became one of the few business leaders to speak at a Security Council meeting, where he reported on his recent meeting with Hamid Karzai and on the infrastructure work Siemens was doing in Afghanistan and Iraq.