Former Chicago police officer Jason Van Dyke was found guilty of murder in the second degree in the shooting death of teenager LaQuan McDonald.
Van Dyke, who is Caucasian, was arrested and charged with first-degree murder after he claimed he shot McDonald 16 times in self-defense on October 20, 2014.
Van Dyke said he spotted the 17-year-old walking down the street, acting erratically while holding a folding knife in his hand.
But dash cam video, which was released a year later after pressure from the local media, showed McDonald walking away from Van Dyke when the officer opened fire.
After the verdict was read on Friday, protesters cheered outside the courthouse. Van Dyke's wife broke down and cried in the courtroom as the former cop was taken away in handcuffs.
McDonald's great-uncle also cried in the courtroom.
Van Dyke faces a minimum of 10 years in prison.
The city of Chicago reached a financial settlement with McDonald's family for an undisclosed sum.
An earlier version of this post was edited to correct Van Dyke's possible prison sentence.