Knox, 24, and her former Italian boyfriend, Raffaele Sollecito, 27, were convicted in December 2009 of sexually assaulting and murdering Meredith Kercher in Perugia, Italy in 2007. Knox was then sentenced to 26 years in prison. At the time of the murder, Kercher and Knox were roommates.
Sollecito's conviction was also overturned, CNN reports. The jury upheld Knox's separate conviction on defamation charges.
One of Knox's lawyers, Carlo Dallas Vedova, told CNN that Knox will be leaving Italy "as soon as possible."
"Amanda is released," he said. "She wants to go back home. She has always confirmed that she was a friend of Meredith."
According to The New York Post, Knox "collapsed in tears after the verdict was read." She did not speak to reporters as she left the courthouse in Perugia. As a result of the defamation charges, she will have to pay compensation to bar owner Patrick Lumumba, whom she initially blamed for the murder.
After the court decision a number of people gathered outside the Perugia courthouse shouting “Vergogna!”, shame, and booing in front of hundreds of TV cameras. The judges, meanwhile, were escorted outside the building by police agents.
One of Sollecito's lawyers, Italian MP Giulia Bongiorno, said on Italian TV Rainews afterward that she didn't blame onlookers who protested against the decision, because intense media coverage had led people to take “visceral” positions on the case. She added that the original guilty verdict was a consequence of a “hasty examination” of the evidence.
The Guardian reports that Knox's sister, Deanna Knox, read a statement to the press following the court decision.
"We're thankful that Amanda's nightmare is over," she said. "She has suffered for four years for a crime that she did not commit."
She thanked her sister's legal team, her supporters and also the court.
"And last, we are thankful to the court for having the courage to look for the truth and to overturn this conviction," Deanna said.
The Kercher family also issued a statement, CNN reports.
"We respect the decision of the judges but we do not understand how the decision of the first trial could be so radically overturned," the statement said. "We still trust the Italian judicial system and hope that the truth will eventually emerge."
According to MSNBC, prosecutors can appeal to Italy's highest court, but as of late Monday there was no sign that they planned to do so. Even if prosecutors do appeal, that would not prevent Amanda from returning home to the United States.
The New York Times reports that hundreds of journalists were in the courtroom on Monday to witness the end of a 10-month appeals trial that has received worldwide attention. The court had a choice to acquit both Amanda and Sollecito, to confirm the sentences or even to increase them.
Prosecutors had asked that both sentences be increased to life imprisonment.
From the Times: In a final address to the court on Monday morning, Luciano Ghirga, one of Amanda's lawyers, made repeated references to the findings of court-appointed experts that challenged key evidence in the prosecution’s case – DNA on a knife and a bra clasp that prosecutors say place Amanda and Sollecito at the scene of the crime. The independent review suggested that the DNA samples might have been contaminated and in any case could not be definitely linked to the defendants.
Earlier on Monday, Amanda had declared her innocence and pleaded for her freedom in court.
"I am not what they say I am. I did not kill. I did not rape. I did not steal," Amanda said, according to CNN.
"People always ask 'who is Amanda Knox?' I am the same person that I was four years ago, exactly the same person. The only thing that now separates me from four years ago is my suffering," she also said, in Italian. "In four years, I've lost my friends in the most terrible and unexplainable way. My trust in the authorities and the police has been damaged. I had to face charges that were totally unfair, without any basis. And I am paying with my life for something I haven't done."
In July, Rolling Stone magazine published a detailed piece unpacking the Knox saga. Writer Nathaniel Rich painted Amanda as an "accidental ingénue" with a lot to learn:
Amanda also didn't realize that she would be judged by her behavior, her looks and her nationality. Nor did she suspect that her faith in human nature was a dangerous fantasy. She would learn other terrible lessons along the way too — the kinds of things most of us don't like to think about. In July, while she waits for her appeal case to be settled, Knox will turn 24. It will be her fourth consecutive birthday in jail. She's learned her lessons. Now she just wants to go home.