In his new role, Gellett, who was also founder of ZGC, will be responsible for the day-to-day running of the business as well as driving new business.
TCA chief executive Robert Preveser said: "In the short time that John has been with TCA, he has already had a positive impact on our infrastructure and new-business opportunities, allowing me to continue focusing on helping our clients build their business. His ability to get a job done with little fuss, but with a huge impact, is undeniable."
TCA is understood to be expanding, with a raft of new hirings expected in the coming weeks to help it cope with the new business that has been generated as a result of Gellett's appointment.
Gellett said: "TCA had such a great client base and fantastic proposition that it seemed right to merge our vision to tap the blatant potential that exists for the agency. I'd rather be in there working and planning with clients, helping their business to grow, rather than just running an agency. At TCA, I have been given that opportunity and look forward to the mixture of fund and hard work ahead."
Gellett was a founding member of the Marketing Team, a subsidiary of the KLP Group. In 1989, he set up marketing services agency ZGC, which was one of the below-the-line agencies taken over by Canadian marketing firm Mosaic to form Mustard. Mustard was renamed Mosaic UK in 2001 and folded last year when its parent got into financial difficulty.
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