"Ashley and Mary-Kate have grown up to become America's young style icons. They have an amazing sense of fashion and individuality that intrigued us," the design duo of Mark Badgley and James Mischka said Wednesday in a statement.
The Olsens attended Badgley Mischka's fall preview at New York Fashion Week. The designers said the 19-year-old actresses "reflect the younger, edgier and more sensual glamour that we have incorporated in our latest fall collection."
Print ads featuring the Olsens will appear in the April issues of Vogue, Elle, InStyle and Vanity Fair magazines. In addition to the print ads, the campaign will appear in stores and on the Internet.
Gilles Bensimon photographed the twins — Mary-Kate is a brunette and Ashley is blond — in the presidential suite of the St. Regis Hotel in Manhattan.
"We have been fans of Mark and James for years and were honored when approached to appear in the campaign," Ashley said in a statement.
Mary-Kate described the clothes in the fall collection as "glamorous, beautiful, colorful and fun."
The designers have worked with famous twins before: They dressed Barbara and Jenna Bush for last year's inaugural ball.
Since sharing the role of Michelle Tanner on the '80s comedy "Full House," the Olsens have created a multimedia empire, Dualstar Entertainment Group, with a clothing line, movies, DVDs and other merchandise.
The ad campaign will be the first time they have promoted a brand outside of their own company, said Iconix Brand Group Inc., which markets and licenses the Badgley Mischka trademarks on a variety of apparel and fashion products.
Both sisters were enrolled at New York University, but Mary-Kate, who spent six weeks at a treatment center for an eating disorder in the summer of 2004, took a leave of absence early in her sophomore year in 2005 to devote more time to her business.
Last month, Mary-Kate was targeted by acid-tongued fashion critic Mr. Blackwell in his 46th annual "Worst Dressed" list. He called her clothes "bag lady rags" and "depressingly decayed."