A reputed gangbanger who cornered and then shot an undercover FBI agent has been found guilty by a federal jury in Brooklyn.

The panel deliberated over three days before convicting Ronell Watson Wednesday on charges of attempted murder of a law enforcement officer, assault and the use of a firearm.

FBI Special Agent Christopher Harper missed the reading of the verdict by mere minutes, but pumped his fists and hugged a court officer when told by The Post that Watson had been found guilty on all counts. He declined to comment on the verdict.

Watson’s family also declined to speak to reporters as they left court.

In a rare move, the US attorney for the Eastern District of New York, Richard Donoghue, prosecuted the case himself, arguing that the 31-year-old reputed Crips member intended to kill Harper as he sat in a parked car in front of Watson’s Canarsie home while working surveillance.

Harper was shot in the back before returning fire, catching Watson in the hand. Both men survived.

Watson faces up to life behind bars when sentenced.

“What was said in court was more than enough,” one juror who declined to give her name said as she left the courthouse.

Other jurors declined to comment.

Defense attorney Michelle Gelernt of the Federal Defenders did not immediately return a message.