The court found on Wednesday that Knox had wrongly accused an innocent man, the Congolese owner of the bar where she worked part time, of the killing. But she will not serve any more jail time, given the three-year sentence counts as time already served.
Knox, who had returned to Italy for only the second time since she was freed in 2011 to participate in the trial, showed no visible emotion as the verdict was read aloud.
But her lawyer, Carlo della Vedova, said shortly afterward that "Amanda is very embittered".
Knox had written on social media ahead of the hearing that she hoped to "clear my name once and for all of the false charges against me. Wish me luck".
The slaying of 21-year-old Meredith Kercher in the idyllic hilltop town of Perugia fuelled global headlines as suspicion fell on Knox, a 20-year-old exchange student from Seattle, and her new Italian boyfriend of just a week, Raffaele Sollecito.
Flip-flop verdicts over nearly eight years of legal proceedings polarised trial watchers on both sides of the Atlantic as the case was vociferously argued on social media, then in its infancy.
Knox's retrial was set by a European court ruling that Italy violated her human rights during a long night of questioning days after Kercher's murder, deprived of both a lawyer and a competent translator.
Earlier in the hearing, Knox had asked the eight Italian judges and civil jury members to clear her of the slander charge.
In a soft and sometimes breaking voice, Knox had told the court that she wrongly accused Patrick Lumumba under intense police pressure.
"I am very sorry that I was not strong enough to resist the pressure of police,'' Knox told the panel in a nine-minute prepared statement, sitting alongside them on the jury bench.
"I didn't know who the murderer was. I had no way to know."
The case continues to draw intense media attention, with photographers massing around Knox, her husband Christopher Robinson and their legal team as they entered the courtroom about an hour before the hearing.
A camera knocked her on the left temple, her lawyer Luca Luparia Donati said. Knox's husband examined a small bump on her head as they sat in the front row of the court.
Despite Knox's exoneration and the conviction of an Ivorian man whose footprints and DNA were found at the scene, doubts about her role persisted, particularly in Italy. That is largely due to the accusation she made against Lumumba.
Knox is now a 36-year-old mother of two small children. She returned to Italy for only the second time since she was freed in October 2011, after four years in jail, by a Perugia appeals court that overturned the initial guilty verdict in the murder case against both Knox and Sollecito.
She remained in the United States through two more flip-flop verdicts before Italy's highest court definitively exonerated the pair of the murder in March 2015, stating flatly that they had not committed the crime.
In the fall, Italy's highest Cassation Court threw out the slander conviction that had withstood five trials, ordering a new trial, thanks to a 2022 Italian judicial reform allowing cases that have reached a definitive verdict to be reopened if human rights violations are found.
This time, the court has been ordered to disregard two damaging statements typed by police and signed by Knox at 1.45am and 5.45am as she was held for questioning overnight into the small hours of November 6, 2007.
In the statements, Knox said she remembered hearing Kercher scream, and pointed to Lumumba for the killing.
Hours later, still in custody about 1pm, she asked for pen and paper and wrote her own statement in English, questioning the version that she had signed.
"In regards to this 'confession' that I made last night, I want to make clear that I'm very doubtful of the verity of my statements because they were made under the pressure of stress, shock and extreme exhaustion," she wrote.
