Randy "Cowboy" Therrien was sentenced in federal court in connection with two murders and plots to kill two other people for the prison-based gang also known as La Eme, Spanish for the letter M.
David "Smilon" Gallardo received a life sentence plus 300 months for his involvement in the crimes.
Jurors in May convicted Therrien, Gallardo and 10 other reputed Mexican Mafia members and associates, who were charged under a federal racketeering law.
It was the first case in which the Racketeer Influenced and Corrupt Organization statute was used against the gang.
Another man indicted in the case was acquitted.
Prosecutors charged that the gang has up to 400 members and that it used violence to punish enemies and to control drug sales by Hispanic street gangs in Southern California.
Defense attorneys denied the gang exists. Outside court, Therrien's defense attorney, Morton Boren, denounced the sentence.
"I mean, what is the Mexican Mafia?" Boren said. "There may be a group of individual guys who called themselves 'the Mexican Mafia.' But this case isn't going to stop anybody else from calling themselves that, either."
U.S. District Judge Ronald S. Lew was expected to take about three days to sentence all 12 defendants. Assistant U.S. Attorney Lisa Lench refused to comment about the sentence.
Mexican Mafia Members Get Life in Prison
LOS ANGELES, Updated 4:45 p.m. September 2, 1997 -- Two reputed Mexican Mafia members were sentenced to life in prison without parole on Tuesday for murder, racketeering and extortion.