Shepherdson, who left Topshop in 2006, will become chief executive of the chain as part of the management buy in with former Topshop colleagues Keith Wilks and Jo Farrelly, who join as finance director and marketing director respectively.
Whistles will be spun out of Mosaic Fashion but Baugur has retained an interest in the chain. Shepherdson and her team are understood have taken a significant stake in the business.
Shepherdson said: "This is a very exciting venture. I am thrilled to be taking over such an established British brand with enormous potential. I look forward to drawing on the brand's heritage and developing it into an exciting and stimulating collection and store environment. We see a great
opportunity to create something unique for the woman who loves great design, isn’t scared of a little edginess and who wants to reference but not slavishly follow trends."
Derek Lovelock, chief executive of Mosaic Fashions, said: "Whistles is a great brand which has grown strongly under the leadership of Amanda Burrows [Whistles brand director] and her team. However, given Mosaic’s strategy to build scaleable international brands we believe that Jane and her team will have the focus and resources to take Whistles to its next level."
Shepherdson, credited with having revolutionised Topshop, has advised several non-profit organisations including fair trade and ethical clothing brand People Tree and Oxfam since leaving Topshop.
Burrows will stay as Mosaic Fashions but it is unclear what her new role will be.
Whistles was bought by Mosaic Fashions in 2004, and has more than 40 standalone stores in the UK, and around 40 concessions in department stores.