It was the first time the court has revered a death penalty this year. Twenty-four other death penalty appeals were affirmed by the court in 2011.
Johnson was the leader of the 89 Family Bloods gang in the 1980s and early '90s. Johnson is believed to have led the 80 gang members who were responsible for more than 60 murders on their South-Central L.A. turf.
Johnson was convicted in 1997, along with Michael "Fat Rat" Allen, of murdering two rival gang members six years earlier. Prosecutors allege that Johnson ordered Allen to kill the rivals with an Uzi.
During deliberations, two jurors told the judge they were concerned a third juror had made up his mind before all testimony was heard. After the judge interviewed the entire jury, the juror was removed from the trial for prejudging the case and relying on evidence not presented during the trial.
That juror was replaced with an alternate juror. The new jury found Johnson and Allen guilty of first-degree murder and recommended the death penalty for both. Los Angeles Superior Court Judge Charles Horan adopted the jury's recommendation in December 1997.
The replaced juror had reportedly told his colleagues that he didn't believe one of the witnesses who testified that he wasn't at work at the time of the killing because a Hispanic co-worker had punched his time card for him.
"That's a lie. I know Hispanics, they never cheat on timecards, so this witness was at work, end of discussion," the replaced juror was quoted as saying.
A unanimous Supreme Court found that comment didn't amount to relying on outside evidence.
Every death sentence is automatically appealed to the state's high court. There are 720 inmates on California Death Row.
Los Angeles prosecutors will have to seek a new trial if they want to reinstate those convictions and death penalties. The office said it was reviewing the ruling.
Love said Johnson was on death row for five years before getting a lawyer to handle his appeal, and the California Supreme Court waited many more years to decide the case after it had been fully briefed.
The Associated Press contributed to this report.