Entertainer had served two years of a maximum ten year sentence for sexual assault
Mr Cosby had served two years of a three to ten year sentence for drugging and attacking Andrea Constand at his home in 2004.
The court ruled that an agreement that Mr Cosby had made with a previous prosector meant that he could not be charged in the case.
He was convicted of sexual assault at a retrial in 2018, and denied parole earlier this year for failing to take part in any sexual offender programmes in prison.
Mr Cosby said that he would rather serve all ten years behind bars than show any regret, and has always insisted that his encounter with Ms Constand was consensual.
Mr Cosby did not speak at the press conference.
“We’ve said from day one, we just didn’t think he was treated fairly. And that…the system has to be fair, and fortunately the Supreme Court agreed with us,” said one of his lawyers Brian Perry.
“He’s happy, his wife is happy. The system only works if it’s fair to all sides. That’s the bottom line.”
The current Montgomery County District Attorney, Keith Steele, who brought the charges against Mr Cosby in 2015, earlier attacked the court’s ruling.
“He was found guilty by a jury and now goes free on a procedural issue that is irrelevant to the facts of the crime,” said Mr Steele in a statement.
And he praised Ms Constand “for her bravery in coming forward and remaining steadfast throughout this long ordeal, as well as all of the other women who have shared similar experiences.”
And he added: “My hope is that this decision will not dampen the reporting of sexual assaults by victims.
“Prosecutors in my office will continue to follow the evidence wherever and to whomever it leads. We still believe that no one is above the law — including those who are rich, famous and powerful.”
Ms Constand reported Mr Cosby to the police in 2005, a year after the alleged attack, but then-District Attorney Bruce Castor, who defended Donald Trump at his second impeachment trial earlier this year, declined to press charges.
Mr Cosby then gave a deposition in the civil suit brought against him by Ms Constand, which he settled for more than $3m in 2006.
In 2015 a federal judge unsealed the testimony given in that case, which was used by the current District Attorney to re-open Mc Constand’s case.
The Pennsylvania Supreme Court has said that Mr Cosby cannot be retried on the same charges.