Huxtable joined 23red in the newly created post of managing director in May 2010 from CHI & Partners were he was business director.
He has left 23red to join social media technology company Engage Sciences as chief revenue officer, responsible for the commercial and marketing divisions.
Working closely with managing partners Jane Asscher and Sean Kinmont, Huxtable was responsible for expanding the marketing agency’s portfolio of public and private clients.
However, over the last year the agency has been hit hard by the COI cuts, which account for a significant portion of its business, with clients including Change 4 Life, HM Revenue & Customs and drinkaware.co.uk.
The agency is now looking for a replacement for Huxtable. Meanwhile 23red has said its finance director will broaden his role to become commercial director and Jane Asscher will be fulfilling a more active chief executive role. She will work closely with group account director Nicola Nimmo and Rachel Tattersdill.
Huxtable joined CHI as an account director in 2007 and headed up its RBS account. He oversaw the ad agency's Waterstones and English Heritage accounts and helped it secure the Green Flag account.
In July 23red announced the former IPA director-general Hamish Pringle will return to the agency scene by becoming its strategic advisor. He joins to work as a contact between the agency and its most senior clients as well as helping its new business drive.
Huxtable said: "23red is a great agency but it never really got its light from out of the bush. However, now with Hamish joining, it will give them opportunity to do that and I wish them every success."