Davis was convicted of two counts of first-degree murder and conspiracy to commit murder and robbery.
Brown released a letter outlining his decision to reverse a parole board hearing that found Davis eligible. The governor found it encouraging that Davis had behaved well in prison, earning advanced college degrees and participating in individual and group improvement programs.
But Brown believes Davis still has not fully accounted for his crimes, citing statements from Davis as recently as 2012 in which he makes new admissions in the murder cases of Donald Shea and Gary Hinman. He also finds the brutality of the murders were exceptional.
"As our Supreme Court has acknowledged, in rare circumstances, a murder is so heinous that it provides evidence of current dangerousness by itself. This is such a case," wrote Brown.
"I have considered the evidence in the record that is relevant to whether Mr. Davis is currently dangerous. When considered as a whole, I find the evidence I have discussed shows why he currently poses a danger to society if released from prison. Therefore, I reverse the decision to parole Mr. Davis," Brown wrote.
The Manson Family, led by Charles Manson, went on a murder spree beginning in 1969.
Davis was not involved in the notorious Sharon Tate-LaBianca killings but was convicted with Manson and others in the murders of musician Hinman and a stuntman, Shea.
Steve Grogan, another participant in those killings, was released years ago after agreeing to lead police to where the bodies were buried on a ranch in the San Fernando Valley.
Davis was 30 years old when he was sentenced to life in prison in 1972. He has long claimed he was only a bystander in the killings of the two men, but has acknowledged his shared responsibility in recent years.
Davis became a born-again Christian in prison and ministered to other inmates, married a woman he met through the prison ministry, and has a grown daughter. The couple recently divorced. He also earned a master's degree and a doctorate in philosophy of religion.
Manson and three of his followers, Leslie Van Houten, Patricia Krenwinkel and Charles "Tex" Watson, remain in prison for life in the Tate-LaBianca killings. Their co-defendant, Susan Atkins, died of cancer behind bars in 2009.
The Associated Press contributed to this report.
