Tidmarsh is currently head of factual marketing and is a former head of the intellectual property management unit responsible for the marketing of factual programmes.
Last week, the BBC again denied that it had invited any bids for the sale of BBC Worldwide after comments at the RTS International Conference made by Bob Iger of Disney were read otherwise.
The BBC said that as part of a wide-ranging review process, it is talking to the industry for their views on all our commercial businesses.
This review has not yet completed and no decisions have been made.
A spokesman said: "We will be putting recommendations from the review to the executive and board of governors later this year."
Tidmarsh will oversee Worldwide's marketing projects including non-children's TV and consumer publishing-related projects, as well as shaping the company's investment strategy.
Following her departure, the IPM unit will be merged with the marketing services department under a new head of creative services Farhana Gani. The new integrated marketing operation under Gani will report directly to Tidmarsh.
Mike Phillips, managing director of BBC international television, said: "The role brings, for the first time, our strategic market planning and the creative execution of campaigns together under a single management, with a clear remit that will be more easily understood by our partners in the BBC and in the wider production community."
Tidmarsh joined BBC Worldwide in 1998 as brand manager for the BBC natural history unit.
As head of the IPM unit, Tidmarsh managed the global marketing of award-winning brands including 'The Human Body', 'Walking with Dinosaurs', 'The Blue Planet' and David Attenborough's 'Life of Mammals'.
The BBC has allegedly been in talks with media giants including Time Warner, Disney and Bertelsmann, to discuss selling off parts of its commercial, sales and publishing arm, BBC Worldwide, which is valued at a total of £2bn.
BBC Worldwide owns 10 channels including UKTV stations, BBC America, and 26 magazines. Last year, it had revenues of £657m and generated £141m profit, which was ploughed back into the BBC.
The corporation is understood to be considering a possible break-up of the company, which also owns merchandising operations and overseas programme sales, rather than an outright sale.
The deal would be timed to coincide with a government study of BBC funding, which would be crucial to its Charter Renewal.
If you have an opinion on this or any other issue raised on Brand Republic, join the debate in the .