State Attorney Willie Meggs made the announcement at a news conference, saying the woman's memory lapses of the events last December were problematic and there was not enough evidence to win a conviction. The woman told police she had been drinking at a bar with friends before the alleged assault took place at an off-campus apartment.
"It's not inconsistencies, it's lack of memory most of the time," Meggs said of the woman's allegations.
While the alleged assault happened last December, reports didn't surface in the public until November, as the redshirt freshman was well into a remarkable season with Florida State.
Winston, 19, has led the Seminoles to a No. 1 ranking and a shot at a national championship if they defeat Duke on Saturday in the ACC championship game. As for the Heisman, many voters were waiting to see whether he would be charged before the deadline for ballots Monday. The trophy for the nation's top player will be awarded Dec. 14.
Meanwhile, the woman's family was sharply critical of the Tallahassee Police Department, accusing the agency of delaying the investigation and discouraging her from going forward with the case because of the public attention it would receive.
"The victim has grave concerns that her experience, as it unfolded in the public eye and through social media, will discourage other victims of rape from coming forward and reporting," according to a statement from the accuser and her family.
The Associated Press does not identify alleged victims of sexual assault.
The alleged assault was reported to police Dec. 7, 2012, but it wasn't until last month before the public had any idea Winston was the subject of a sexual assault investigation. And it wasn't until Thursday that specific details of the woman's accusations began to emerge.
She told police she and friends had five to six shots at a bar and her "memory is very broken from that point forward," according to a search warrant for cellphone records. She said she remembered being in a cab with a "non-descript" black man and going into an apartment, but she didn't remember where it was.
The warrant said she tried to fight the man off, and at some point, another man came into the room and told him to stop. But the two went into a bathroom "where he completed the act."
Her next memory was of the suspect dressing her, putting her on a scooter and dropping her off at a campus intersection.
The woman told police she initially didn't know who assaulted her. She identified Winston, who is black, about a month after the alleged assault.
Meggs' office took over the case last month and interviewed the accuser. They also took DNA from Winston and matched it to DNA on the woman's underwear. They also matched DNA on her shorts to her boyfriend at the time.
Winston's attorney, Timothy Jansen, said Winston had consensual sex with the accuser. Winston refused to be interviewed by police and has not talked about the case to the media.
The quarterback said in a statement he was relieved.
"It's been difficult to stay silent through this process, but I never lost faith in the truth and in who I am," Winston said.
The accuser's family has been sharply critical of the way Tallahassee police have handled the case. They said they pushed to have a DNA sample taken from Winston, only to be told by a police detective that it would alert Winston and make the case public. The family said Carroll was warned by police that Tallahassee is a "big football town, and the victim needs to think long and hard before proceeding against him because she will be raked over the coals and her life will be made miserable."
Tallahassee police have defended their handling of the case and said it was placed on inactive status in February after police were told the alleged victim did not wish to prosecute the case. The woman's attorney has denied that the woman wanted to drop the investigation.
The alleged victim was an FSU student, but she left school last month as media reports of the case surfaced. Meggs said when his office spoke with the woman last month, she wanted the case to move forward.
At a restaurant on campus, students high-fived one another and did the Seminole's chant and tomahawk chop when Meggs' said no charges would be filed.
"It's been a tough couple weeks," said Justin Savage, a 21-year-old senior sports management major from Fort Walton Beach. "I'm just so grateful. He's just so lovable a guy. You can see him on campus and he'll talk to you, it doesn't matter who you are."
Associated Press writer Kareem Copeland contributed to this story.
Follow Gary Fineout on Twitter: http://twitter.com/fineout.Suggest a correction