He leaves the role with no job to go to. He will serve six months of gardening leave before deciding on his options.
Sources close to Marsden speculated he may be considering a move to COI, where he has close contacts, but he would not confirm this.
Marsden said: "It feels like a good time to leave. There is still a great deal I want to do. I am sure it will be outside of the soft drinks category."
He added that his departure would not affect the brand's existing agency relationships. CHI & Partners handles its advertising, and MindShare works on Britvic's media.
The Britvic chief executive, Paul Moody, added: "Andrew is one of our longest-serving directors. He has been a key figure in the development of our business."