The verdict prompted tears from the parents of victim Daunte Wright and a jubilant celebration by supporters outside the courthouse who chanted "Guilty, guilty, guilty!".
The mostly white jury deliberated for about 27 hours over four days before finding Kim Potter guilty of first and second-degree manslaughter for the killing during a traffic stop.
Potter, 49, faces about seven years in jail under Minnesota sentencing guidelines, but prosecutors are seeking a longer term.
Potter shot and killed 20-year-old Wright during an April 11 traffic stop as she and other officers were trying to arrest him on an outstanding warrant for a weapons possession charge.
Jurors saw video in which Potter repeatedly said she would Taser Wright, but instead shot him once in his chest with her gun, which was in her hand.
"(Expletive)! I just shot him. ... I grabbed the wrong (expletive) gun," she said on the video. Moments later, she said: "I’m going to go to prison."
During her sometimes tearful testimony, Potter told jurors that she was "sorry it happened." She said the traffic stop "just went chaotic”.
Her attorneys claimed the shooting was a tragic mistake.
But after jurors found Potter guilty, Judge Regina Chu ordered her taken into custody and held without bail.
Speaking outside the courthouse, Daunte Wright’s mother said the verdict triggered "every single emotion that you could imagine."
"Today we have gotten accountability and that’s what we’ve been asking for from the beginning," Katie Bryant said, crediting supporters for keeping up pressure.
"We love you, we appreciate you, and honestly, we could not have done it without you," she said.
Prosecutors say they will seek to prove aggravating factors that merit an “upward departure” from sentencing guidelines of seven years in jail for Potter.
They allege her actions were a danger to others, including her fellow officers, to Wright’s passenger and to the couple whose car was struck by Wright’s after the shooting.
They also allege she abused her authority as a police officer.