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Kate, 31, came out on top with 338 votes, followed by designer Victoria in second, with 185.
Cheryl Cole and Kate Moss were third and fourth respectively in the poll, conducted by StyleinView.co.uk, ahead of Kelly Brook and Lady Gaga, known for her more outlandish approach to fashion.
Rihanna and Zooey Deschanel came in seventh and eighth place, with former TOWIE star Amy Childs and model-of-the-moment Cara Delevingne rounding up the top ten.
Preceding Kate's royal flair for fashion, Princess Diana was also named on a list of the most fashionable icons of all time, beaten only by the indisputable classic style of Audrey Hepburn.
Prince William's adored late mother was named ahead of Marilyn Monroe in third place and Jackie Kennedy in fourth in the poll, that demonstrated that classic, feminine style reigns supreme.
Coco Chanel, Elizabeth Taylor and Katherine Hepburn also featured in the top ten alongside the late Margaret Thatcher, a surprise addition to the list.
Co-founder of StyleinView.co.uk, Dexter Grima, said, "We were not surprised to see Kate Middleton, Duchess of Cambridge, crowned the most fashionable celebrity as she has demonstrated a keen eye for knowing what suits her and dressing for the occasion, similar to Princess Diana.
"From her wedding day style to more formal royal appointments, and even her maternity choices, Kate has remained consistent. Her influence has been reflected in the items our users are searching for on StyleinView.co.uk with a significant increase in searches for Kate Middleton inspired dresses and bikinis."
Top 10 Most Fashionable Icons
1. Kate Middleton
2. Victoria Beckham
3. Cheryl Cole
4. Kate Moss
5. Kelly Brook
6. Lady Gaga
8. Zooey Deschanel
9. Amy Childs
10. Cara Delevigne
Top 10 Most Fashionable Icons of All Time
1. Audrey Hepburn
2. Princess Diana
3. Marilyn Monroe
4. Jackie Kennedy/Onassis
5. Coco Chanel
6. Brigitte Bardot
7. Elizabeth Taylor
8. Katharine Hepburn
9. Vivienne Westwood
10. Margaret Thatcher