Scott, a former model whose sexy gowns were favourites among A-list Hollywood stars such as Nicole Kidman, Amy Adams and Penelope Cruz, was found hanging from a scarf in her apartment.
A spokesperson for Jagger said he was “completely shocked and devastated” by the news.
The glamorous pair had been dating since 2001 and were often seen at celebrity events, with the tall, leggy Scott towering over Jagger.
Police confirmed that a female was found “unconscious and unresponsive” in an apartment building in Manhattan’s upscale Chelsea area. The stylish high-rise building where Scott lived was cordoned off.
Julie Bolcer, of the city’s Office of the Chief Medical Examiner, said they had been notified of a deceased person at Scott’s address, but had not received the body nor begun work to determine the manner of death.
“Given the timing, that individual will probably be examined tomorrow and if everything is straight forward, the cause and manner of death would be available by tomorrow,” she said.
Scott cancelled a planned show for her eponymous fashion label at London Fashion Week last month and decided to give private appointments instead.
Scott, who was born Luann Bambrough, was raised in Utah by adoptive parents. The dark-haired beauty started her career as a model in Paris before becoming a stylist and designer. She designed a small collection for Banana Republic stores last year.
Her love of fashion began when she made her own clothes as a teenager, according to her website. As a model in Paris, Scott said she became more interested in making clothes than modelling them.
After moving to Los Angeles, she worked as a stylist and designed privately before creating her own collection.