Reynish, 35, a New Zealander, has worked for the fast food chain for seven years, mainly in New Zealand and Australia, where he was most recently head of marketing.
He joined the UK team Two months ago as senior marketing manager and has now been promoted to head of marketing, with all members of the UK marketing team reporting directly to him.
Reynish will report to Andre Lacroix, general manager for UK and Ireland and president of Burger King International.
He takes up the role as Burger King faces a new era following its acquisition by a consortium of venture capitalists in December. The sale by former parent Diageo to Texas Pacific Group, Bain Capital and the venture arm of Goldman Sachs followed a protracted takeover process.
The final price was £945m, around a third less than the original one considered by the two parties and reflects the troubled state of the fast food market, in which both Burger King and McDonald's are struggling to maintain profits.
Operating profits for Burger King fell 29% to £79m over the six-month period ending December 31, below market expectations.
Reynish told Marketing he would not be reviewing UK agency relationships, including creative - held by Delaney Lund Knox Warren - and media - held by Carat. "My plan is to sell more hamburgers as quick as I can," he said.
"I hope people will perceive the brand in a far stronger way, on whatever level, in a year's time. We have got to add value to this brand, and I know we can do it."
Anna Joseph left Burger King before Christmas, just three months after joining as marketing director from Marks & Spencer (Marketing, December 19, 2002). She is joining consultancy Eden McCallum. Her resignation is said to be have been sparked by differences with global marketers over strategy.