Ahmaud Arbery, 25, was shot on 23 February 2020 in a confrontation with Travis and Gregory McMichael and their neighbour, William Bryan.
The defendants said they acted in self-defence during a citizen's arrest; prosecutors said race was a factor.
The men now face minimum sentences of life in prison.
A mainly white jury of 12 deliberated for about 10 hours before returning their verdict at around midday on Wednesday.
The trio were found guilty of murder, aggravated assault, false imprisonment and criminal intent to commit a felony.
In February the three men will face another trial in a federal hate crimes case, alleging that they targeted Arbery because he was black.