Scott, who was dating rocker Mick Jagger, was found dead in her Manhattan apartment by her assistant on Monday morning.
"The manner of death was determined to be suicide," said a spokesperson for the medical examiner's office.
One of the most influential designers, Scott had celebrities like Nicole Kidman, Julianne Moore, Sarah Jessica Parker and the late Elizabeth Taylor as her clients.
A shocked Jagger, who was in Australia for a Rolling Stones tour, rushed back to New York upon hearing the tragic news.
In his tribute, Jagger said: "I am still struggling to understand how my lover and best friend could end her life in this tragic way."
The Rolling Stones tour of Australia and New Zealand has been postponed now.
Scott, 49, was said to be going through a difficult period financially at the time of her death. She had cancelled her upcoming London show due to production delays last month and had planned to unveil her fall 2014 collection via social media in early March, but that too was delayed.
Her company was in debt to the tune of USD 6 million and she was apparently set to announce the closer of her business.