The punishment handed down all but completed the dizzying, late-in-life fall from grace for the comedian, former TV star and breaker of racial barriers, who was led from the court in handcuffs.
Cosby is the first celebrity of the “MeToo” era to be sent to prison.
“It is time for justice,” Montgomery County Judge Steven O’Neill said in sentencing on Tuesday.
“Mr Cosby, this has all circled back to you. The time has come.”
The judge quoted from victim Andrea Constand’s own statement to the court, in which she said Cosby took her “beautiful, young spirit and crushed it”.
Cosby declined the opportunity to speak before the sentence came down, and afterward he sat smiling, laughing and chatting with his defence team.
His wife of 54 years, Camille, was not in court.
Constand smiled broadly upon hearing the punishment and was hugged by others in the courtroom.
Cosby’s lawyers asked that he be allowed to remain free on bail while he appeals his conviction, but the judge appeared incredulous over the request and turned it down.
The judge said that even considering Cosby’s age and blindness, “he could quite possibly be a danger to the community”.