Hagger, who resigned last week, joined Wunderman as managing director last November from Possible where she was managing director, a post she had held for only six months. The move followed Possible's move into Wunderman within WPP.
Before Google, Hagger was head of digital and technology at The Lighthouse Company. She was chief marketing officer at SapientNitro (now SapientRazorfish) EMEA between 2012 and 2013, and was briefly head of digital at AAR in 2012.
Hagger spent 11 years at Glue London (now Isobar UK) from 2000 in roles including managing director and chief integration officer.
Pip Hulbert, chief executive of Wunderman UK, confirmed Hagger's departure and added: "She is now moving on to pursue interests outside of the agency, and she leaves with our best wishes."
Hulbert confirmed the agency would be looking for a replacement to fill Hagger's position.
Hagger was unable to disclose her next move but said: "I'm leaving to pursue exciting opportunities beyond agency life that will enable me to achieve true work-life balance and pursue my life-long learning ambitions."
Of Wunderman she added: "We parted as friends and good colleagues and I'm happy with the good work I managed to achieve while there."