Christopher Bryan Ablett killed Mark "Papa" Guardado outside a bar in San Francisco's Mission District on Sept. 2, 2008.
Prosecutors said the Mongols are an organized criminal motorcycle gang whose primary rival is the Hells Angels motorcycle gang.
According to the Department of Justice, evidence at trial showed that Ablett traveled to San Francisco armed with a foot-long military knife and a .357 magnum revolver. Prosecutors said Guardado confronted him after he learned a person wearing a rival gang's patch was in the Mission District. During the ensuing fight Ablett stabbed Guardado four times and shot him twice, killing him.
The jury didn't buy the defense's claim that the stabbing was in self-defense.
Ablett is scheduled to be sentence in May. He faces a minimum sentence of life in prison.