
Cosby was convicted of aggravated indecent assault in 2018 for drugging and sexually assaulting Andrea Constand in his Pennsylvania home in 2004. He was sentenced to three to 10 years in a state prison.
The Montgomery County District Attorney’s office, which led the high-profile court case against Cosby, said in November that the main question of the appeal centered around the 14th Amendment and the right to due process.
As the decision stands now, it could have “far-reaching negative consequences” across the country, District Attorney Kevin Steele said in a statement.
Jennifer Bonjean, a lawyer for Cosby, had urged the court not to step in.
“Under the unique facts of the case, the Pennsylvania Supreme Court concluded that [the former district attorney] had made an unconditional promise of non-prosecution, and that Cosby had relied on that promise to his detriment, namely foregoing his Fifth Amendment guarantees and testifying at four days of depositions, and that as a matter of fundamental fairness, the promise should be enforced,” she said.
This story has been updated with additional details.