Former Minneapolis police officer Derek Chauvin has been convicted of murder and manslaughter for pinning George Floyd to the pavement with his knee on the black man’s neck.
Chauvin, 45, could now be sent to prison for decades.
The jury comprising six white and six black or multi-racial people came back with its verdict after about 10 hours of deliberations over two days.
Chauvin was found guilty on all charges: second-degree unintentional murder, third-degree murder and second-degree manslaughter.
His face was obscured by a Covid-19 mask, and little reaction could be seen beyond his eyes darting around the courtroom.
His bail was immediately revoked and he was led away with his hands cuffed behind his back.
The verdict was read in a courthouse ringed with concrete barriers and razor wire and patrolled by National Guard troops, in a city on edge against another round of unrest — not just because of the Chauvin case but because of the deadly police shooting of a young black man, Daunte Wright, in a Minneapolis suburb on April 11.
The jurors’ identities were kept secret and will not be released until the judge decides it is safe to do so.
Three other former Minneapolis officers charged with aiding and abetting murder in Mr Floyd’s death will stand trial in August.
Mr Floyd, 46, died on May 25 after being arrested on suspicion of passing a counterfeit 20 dollar bill for a pack of cigarettes at a corner market.
He panicked, pleaded that he was claustrophobic and struggled with police when they tried to put him in a squad car. They put him on the ground instead.
The centrepiece of the case was the bystander video of Mr Floyd gasping repeatedly, “I can’t breathe” and onlookers yelling at Chauvin to stop as the officer pressed his knee on or close to Mr Floyd’s neck for what authorities say was nine-and-a-half minutes.
Mr Floyd slowly went silent and limp.
Prosecutors played the footage at the earliest opportunity, during opening statements, with Jerry Blackwell telling the jury: “Believe your eyes.”
And it was shown over and over, analysed one frame at a time by witnesses on both sides.
In the wake of Mr Floyd’s death, demonstrations and scattered violence broke out in Minneapolis, around the country and beyond.
The furore also led to the removal of Confederate statues and other offensive symbols such as Aunt Jemima.
In the months that followed, numerous states and cities restricted the use of force by police, revamped disciplinary systems or subjected police departments to closer oversight.
Chauvin attorney Eric Nelson called a police use-of-force expert and a forensic pathologist to help make the case that Chauvin acted reasonably against a struggling suspect and that Mr Floyd died because of an underlying heart condition and his illegal drug use.
Mr Floyd had high blood pressure, an enlarged heart and narrowed arteries, and fentanyl and methamphetamine were found in his system.
Under the law, police have certain leeway to use force and are judged according to whether their actions were “reasonable” under the circumstances.
The defence also tried to make the case that Chauvin and the other officers were hindered in their duties by what they perceived as a growing, hostile crowd.
Former US president Barack Obama says the conviction of ex-police officer Derek Chauvin over the death of George Floyd was correct, but only one step in the fight for justice.
He said in a statement that true justice requires Americans to understand that “Black Americans are being treated differently every day” and that millions live in fear that their next encounter with law enforcement could be their last.
Mr Obama said the country needs to follow up on the verdict by taking concrete steps to reduce racial bias in the criminal justice system and to redouble efforts to expand economic opportunity in marginalized communities.
Earlier, President Joe Biden, Vice-President Kamala Harris and first lady Jill Biden called members of the Floyd family moments after the verdict, according to video posted by family attorney Ben Crump.
Mr Biden told the family: “Nothing is going to make it all better, but at least now there is some justice.”
He added: “We’re all so relieved.”
Mr Biden said he hoped the verdict would give momentum to congressional police reform efforts.
According to the White House, Mr Biden and Ms Harris watched the verdict live from the private dining room just off the Oval Office.
Hillary Clinton tweeted “Black lives matter” after Derek Chauvin was found guilty of murder over the death of George Floyd in Minnesota.
“George Floyd’s family and community deserved for his killer to be held accountable,” she tweeted.
“Today, they got that accountability.
“Always and forever, Black lives matter.”
David Lammy, Labour’s shadow justice secretary, said: “No judgment can ever make up for murder, but it means everything that justice has been served tonight for George Floyd.
“Let this send a clear message both in the USA and across the world: Black Lives Matter.”
Seven-time Formula One world champion and campaigner Lewis Hamilton tweeted: “Convicting him of all three charges marks a new dawn in the fight for racial justice.
“JUSTICE for George! The emotions I feel right now are hard to describe. Derek Chauvin has been found guilty.
“Convicting him of all three charges marks a new dawn in the fight for racial justice.
“This trial was an opportunity for the justice system to hold Derek Chauvin accountable for his actions when he took the life of George Floyd. We can now breathe a collective sigh of relief that the right decision has been met, and that justice has been served.
“But this is just one step on the path towards a more equal society. Since George’s death, so many other Black people have died at the hands of the police and we must ensure the momentum of today continues.
“The fight isn’t over, and there is more to be done.”