Derek Chauvin, 45, was filmed kneeling on Mr Floyd's neck for more than nine minutes during his arrest last May.
The widely watched footage sparked worldwide protests against racism and excessive use of force by police.
Chauvin was found guilty on three charges: second-degree murder, third-degree murder and manslaughter.
His bail was immediately revoked and he was placed in custody. Sentencing is likely to happen in two months, and Chauvin could spend decades in jail.
In Minnesota, second-degree murder carries a maximum sentence of 40 years in prison. Third-degree murder is punishable by up to 25 years in prison. Second-degree manslaughter is punishable by up to 10 years in prison.