Celebrity website TMZ said the designer -- especially known for her sleek handbags -- hanged herself in her Park Avenue apartment.
A police spokeswoman confirmed Spade committed suicide but told AFP the exact circumstances of her death were not yet clear.
Spade, who first worked as a journalist, including a stint at Mademoiselle magazine, launched her eponymous fashion label in 1993 with her husband Andy. Her cheerful use of bright colors and prints proved a hit with career women.
In the past few years, Spade -- born Katherine Brosnahan -- had launched a new accessories label, Frances Valentine.
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