Branfoot joined the out-of-home specialist in 2006 as sales director and was promoted to managing director at the beginning of 2008, as part of a wider restructure of the company.
He will be retained by Ocean Outdoor as a commercial consultant.
The company said Branfoot had helped "build Ocean over that period into a credible and respected media brand".
Tim Bleakley, chief executive of Ocean Outdoor, said: "It has been a pleasure working with Grant. He is a committed, talented and professional executive who has contributed a lot to the Ocean business since it’s inception. Everyone at Ocean wishes him well for the future."
Bleakley joined Ocean Outdoor in May last year from his position of managing director of sales and marketing at CBS Outdoor.
He took over the post from outdoor veteran Andrew Oldham, who had been appointed chief executive officer on an interim basis following the departure of the previous CEO, Damian Cox.
Ocean Outdoor was founded in 2006 and specialises in high-profile, giant-format outdoor advertising locations across the UK.
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