The company's chairman and founder, David J Moore, has additionally been appointed as CEO and will work alongside Hsu until he leaves his post in October.
Hsu will be moving to the green rewards programme RecycleBank, which is supported by WPP, and will work to introduce green incentive programmes to WPP’s global client base.
He will also become a founding member of the WPP Global Technology Advisory Council.
WPP posted worldwide growth in April, for the first time since the economic downturn hit in 2008.
Its results also showed WPP's specialist digital companies, including 24/7 Real Media, Schematic, Blue Group and Quasar, showing like-for-like growth of more than 9%.