Reynish, who is responsible for the fast-food chain's 拢11m UK marketing budget, leaves at the end of the month. It is not known whether he has a job to go to. He is being replaced by the chain's director of product marketing in the US, Dawn Foster.
Foster is seen as a key figure, having been responsible for developing long-term menu strategies in the US such as adding healthier items and fish and vegetarian products.
Foster also led Burger King's US innovation, including last year's launch of its TenderCrisp and Spicy TenderCrisp chicken sandwiches and the introduction of Fire-Grilled Salads.
Despite criticism levelled at fast-food chains over obesity, the TenderCrisp Sandwich, now on sale in the UK, is reported to contain 780 calories and 45g of fat.
Reynish was responsible for overseeing last June's advertising review, which saw Delaney Lund Knox Warren retain the business, but the 'Got the urge' strapline being axed.
Reynish's exit comes just a month after Andy Brent quit as Burger King International's chief marketing officer. Brent held the role for just one year.