M&C Saatchi will now be placed on Siemens' global advertising roster alongside agencies including Krome and McCann Erickson.
It won the account after a competitive pitch against five UK and international agencies that was handled by the intermediary Cherrypicker out of Siemens' headquarters in Nuremburg, Germany.
Siemens has appointed M&C Saatchi ahead of a major push behind its renewable energy technology.
An initial campaign will involve positioning the division globally and promoting all wind, hydro and solar power products around the world.
Launching later this year, the campaign will target both consumers and a business audience, and is expected to break in Europe before rolling out across Asia and the US.