Harding follows in the footsteps of models Helena Christensen, Rachel Hunter and Penny Lancaster to endorse the range. She is to model lingerie from the latest autumn/winter 2006 collection.
The lingerie and swimwear brand is the brainchild of Scottish entrepreneur Michelle Mone. Since the launch of the original Ultimo bra in 1999, Mone has gone on to invent the Backless Body and Miracle Body.
Mone said: "Sarah had never modelled before, however she was fantastic on the day of the shoot.
"She was signed to appeal to a younger market and to further demonstrate Ultimo's ability to enhance a woman's confidence, both inside and out."
Harding said: "When Michelle asked me to become the new face and body of the brand, I was so honoured and excited. The Ultimo lingerie is gorgeous."
Harding is not the first Girls Aloud member to enter into the promotions world. Bandmate and England football team WAG Cheryl Tweedy fronted a one-off campaign to launch Coca-Cola's Coke Zero brand in July.
The last model to join Ultimo was Christensen, who launched the spring/summer 2006 collection.
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