According to a statement from Matt Seiler, global CEO of UM and member of the office of chairman, Mediabrands, he said that after spending more than 10 years outside of Australia, Stubbs has decided to pursue "other exciting opportunities closer to home".
He added: "During her time at Mediabrands in Asia-Pacific, Ruth has made countless contributions, and although we are very sorry to see her leave, we respect her decision and wish her the very best in her new endeavors."
Stubbs will now be working with Mediabrands in the next few months to manage a proper transition and ensure all client obligations are in order.
During this transition, Mediabrands Asia-Pacific will be led by a regional board structure reporting directly to the office of the chairman.
A decision concerning a new president for Mediabrands is not expected in the immediate future.
Based in Singapore, Stubbs has been with Mediabrands since July 2009. Previously, she worked at GroupM as CEO of Interaction before resigning to replace Jeff Cressall at Mediabrands in April 2009.
Stubbs started her career working with advertising agencies including Ogilvy & Mather and Lowe Lintas in Sydney. Prior to joining GroupM in 2004, she spent 10 years with Euro RSCG Worldwide in a role which was split between heading its digital media operations in US and regional media director based out of Hong Kong.