Sander – best known for her minimalist creations for executive women – said she will now oversee men's and women's apparel at Uniqlo, operated by the Japanese chain Fast Retailing Co Ltd.
"I think you must be surprised to see me here," she told reporters in Tokyo. "But I'm not interested in the past. I'm here for something completely different. The challenge for me is to establish premium quality in a democratically-priced brand.
"My passion has always been quality and pureness. Now I'm looking forward to establishing a new value in a new world," she added.
Sander, whose eponymous fashion label was bought last year by Japan's Onward Holdings Corp, will play a creative advisory role at Uniqlo, Fast Retailing officials said.
The Japanese retail operator hopes the move will further boost Uniqlo's global recognition, which has bucked the recession under the leadership of Forbes-listed chairman Tadashi Yanai.
"Basically this is about how to upgrade Uniqlo, how to really make better clothes, so it's not about making new and separate products," said Fast Retailing operating officer Yukihiro Katsuta.
Sander and Uniqlo designers are working on a special collection to be launched in stores around the world for the autumn/winter season. The clothes are likely to be slightly above the average price range now offered at Uniqlo, said Katsuta.
Sander left her label after it was bought by Italian luxury goods group Prada. London-based investment fund Change Capital acquired the company in 2006 and sold it to Onward last year.