Griffith, who co-founded Work Club in 2007, will be "exploring broader entrepreneurial opportunities" and giving investor advice to start-ups.
Havas acquired a 51 per cent stake in Work Club in 2014. It was reported at the time that the partners –Griffith, Martin Brooks, Jon Claydon, Ben Mooge, Andy Sandoz and Lisa De Bonis – were tied into a six-year earn-out worth up to £30 million.
Before Work Club, Griffith spent almost three years at Agency Republic as the planning director and was the account director at i-level between 1999 and 2004.
Mooge and Sandoz, the creative partners, became the joint executive creative directors at Havas Creative Group in November last year.
Griffith said: "I have loved Havas and Work Club – the work, the clients and the sheer terror of building an agency from start-up.
"After 20 years’ offering advice to clients, it’s time for me to see how much I really know.
"I felt the time was now right for me to change course, as the rest of the Work Club partners continue to shoot for the moon."