Katie Green, who quit her contract after being told she needed to lose two stone, will shoot her first Ultimo campaign this month, joining Melinda Messenger and former Spice Girl Melanie B who also model for the brand.
Green was chosen to model for Wonderbra following a nationwide search to find "real" women to front the lingerie firm's campaign for larger cup sizes.
Her image appeared on posters formed by a mosaic of thousands of images of "real" women photographed during the search, with the copy "D-G. Because we're more than a handful".
However she quit her job after her modelling agency Premier told her that she needed to lose weight and slim down from a healthy size 12 to a size 8-10.
A Wonderbra spokeswoman said: "Wonderbra UK did not ask Katie to lose weight -- in fact we chose her because of her fabulous curves. Since discovering Katie, we have been delighted with how she looked in our new D-G range.
"The model agency that Katie then chose to sign with advised her to lose weight -- advice that Wonderbra would never give to girls."
Despite being told she was too big to model lingerie Ultimo has signed her up to front its campaign for D to G cup bras at Debenhams stores across the country.
Michelle Mone, creator of Ultimo, said: "I was appalled to hear that Katie was told she was too fat to model lingerie. She has an incredible shape and represents real women throughout the UK.
"We're delighted to have her on board -- I'm sure she'll be a huge success and a wonderful ambassador for Ultimo."
Green follows in the footsteps of Rachel Hunter, Helena Christensen and Girls Aloud singer Sarah Harding who have all modelled for Ultimo in the past.