The actor, 80, has been on trial for drugging and assaulting ex-basketball player Andrea Constand in 2004.
Cosby, the first major black actor on primetime TV, will remain out of jail until he is sentenced, the judge ruled.
He unleashed an expletive-filled rant after the verdict, as prosecutors argued he should be denied bail.
The prosecutor argued that he should be held because he is "somebody who has unlimited wealth" and could flee on a private plane.
"He doesn't have a plane," Cosby then erupted, adding a vulgarity which he directed at the prosecutor.
"I feel like my faith in humanity is restored," Cosby accuser Lili Bernard said outside the courthouse.
"We are so happy that finally we can say, women are believed, and not only on #MeToo, but in a court of law," lawyer Gloria Allred said.
It was the second time the actor had stood trial for the allegations, after an earlier jury failed to reach a verdict in June 2017.
At the start of the retrial in Pennsylvania it was revealed that Cosby had paid Ms Constand almost $3.4m (£2.4m) in a civil settlement in 2006.
Cosby is best known for starring in the 1980s TV series The Cosby Show.
Around 60 women over five decades have publicly accused the Emmy award-winning actor of being a sexual predator. But statute of limitation laws mean that only one charge has been brought to trial.
Some of his accusers were present in court, and cried as the guilty verdict was returned.
Cosby's lawyer Tom Mesereau insisted "the fight is not over", adding that he believes Cosby is innocent and that he plans to file an appeal.
Montgomery County District Attorney Kevin Steele, who brought the charges against Cosby, held a press conference after the verdict.
"Money and power or who you are will not stop us from a criminal investigation and prosecuting a case," Mr Steele said, as Ms Constand stood beside him.
When the attack took place, Ms Constand was working as director of operations for the women's basketball team at Temple University, Philadelphia.
She told the court she had gone to the home of her then friend Cosby, to discuss her resignation.
She said he had given her three blue pills to "help take the edge off," which she believed to be a natural remedy.
Minutes later, she was suffering double vision and quickly lost consciousness.
She awoke to find Cosby groping her breasts and penetrating her, she said, adding that the drugs made her physically unable to fight back.
Ms Constand reported the attack, but the district attorney refused to press charges. The case was reopened in 2015.