California Department of Corrections spokeswoman Terry Thornton said that Atkins died late Thursday night. She had been diagnosed with brain cancer in 2008, had a leg amputated and was given only a few months to live.
She underwent brain surgery, and in her last months was paralyzed and had difficulty speaking. But she managed to speak briefly at the Sept. 2 hearing, reciting religious verse with the help of her husband, attorney James Whitehouse.
She had been transferred to a skilled nursing facility at the California Central Women's Facility at Chowchilla exactly one year before she died.
Tate, the 26-year-old actress who appeared in the movie "Valley of the Dolls" and was the wife of famed director Roman Polanski, was one of seven murdered in two Los Angeles homes during the Manson cult's bloody rampage in August 1969.
Atkins was the first of the convicted killers to die. Manson and three others involved in the murders - Patricia Krenwinkel, Leslie Van Houten and Charles "Tex" Watson - remain imprisoned under life sentences. Thornton said that at the time of Atkins death she had been in prison longer than any woman currently incarcerated in California.
Atkins, who confessed from the witness stand during her trial, had apologized for her acts numerous times over the years. But 40 years after the murders, she learned that few had forgotten or forgiven what she and other members of the cult had done.
Debra Tate, the slain actress's younger sister, told the parole commissioners Sept. 2 that she "will pray for (Atkins') soul when she draws her last breath, but until then I think she should remain in this controlled situation." Debra Tate noted that she would have a 40-year-old nephew if her sister had lived.
Atkins' prosecutor, Vincent Bugliosi, had spoken out earlier in favor of release, saying the mercy requested was "minuscule" because Atkins was on her deathbed.
Atkins and her co-defendants were originally sentenced to death but their sentences were reduced to life in prison when capital punishment was briefly outlawed by the U.S. Supreme Court in the 1970s.
During the sensational 10-month trial, Atkins, Manson and co-defendants Krenwinkel and Van Houten maintained their innocence. But once they were convicted, the so-called "Manson girls" confessed in graphic detail.
They tried to absolve Manson, the ex-convict who had gathered a "family" of dropouts and runaways to a ranch outside Los Angeles, where he cast himself as the Messiah and led them in an aberrant lifestyle fueled by drugs and communal sex.
Watson had a separate trial and was convicted.
One night in August 1969, Manson dispatched Atkins and others to a wealthy residential section of Los Angeles, telling them, as they recalled, to "do something witchy."
They went to the home of Tate and her husband. He was not home, but Tate, who was 8½ months pregnant, and four others were killed. "Pigs" was scrawled on a door in blood.
The next night, a wealthy grocer and his wife were found stabbed to death in their home across town. "Helter Skelter" was written in blood on the refrigerator.
"I was stoned, man, stoned on acid," Atkins testified during the trial's penalty phase.
"I don't know how many times I stabbed (Tate) and I don't know why I stabbed her," she said. "She kept begging and pleading and begging and pleading and I got sick of listening to it, so I stabbed her."
She said she felt "no guilt for what I've done. It was right then and I still believe it was right." Asked how it could be right to kill, she replied in a dreamy voice, "How can it not be right when it's done with love?"
The matronly, gray-haired Atkins who appeared before a parole board in 2000 cut a far different figure than that of the cocky young defendant some 30 years earlier.
"I don't have to just make amends to the victims and families," she said softly. "I have to make amends to society. I sinned against God and everything this country stands for." She said she had found redemption in Christianity.
The last words she spoke in public at the September hearing were to say in unison with her husband: "My God is an amazing God." She spent 37 years in the California Institution for Women at Frontera. When she fell ill, she was moved to a medical unit at the Central California Women's Facility in Chowchilla. She died there.
Susan Denise Atkins was born May 7, 1948, in the Los Angeles suburb of San Gabriel. Her mother was stricken with cancer and died when she was 15. Her father, reportedly an alcoholic, sent her and her brother to live with relatives.
While still in her teens, she ran away to San Francisco where she wound up dancing in a topless bar and using drugs. She moved into a commune in the Haight Ashbury district and it was there that she met Manson.
He gave her a cult name, Sadie Mae Glutz, and, when she became pregnant by a "family" member, he helped deliver the baby boy, naming it Zezozoze Zadfrack. His whereabouts are unknown.
The Manson slayings remained unsolved for three months, until Atkins confessed to a cellmate following her arrest on an unrelated charge. Police found Manson and other cult members living in a ranch commune in Death Valley, outside Los Angeles.
Besides Tate, their other victims were celebrity hairdresser Jay Sebring, coffee heiress Abigail Folger, filmmaker Voityck Frykowski and Steven Parent, a friend of Tate's caretaker; and grocery owners Leno and Rosemary LaBianca. Atkins also was convicted with Manson of still another murder, of musician Gary Hinman, in July 1969.
Atkins married twice while in prison. Her first husband, Donald Lee Laisure, purported to be an eccentric Texas millionaire. They quickly divorced. Whitehouse, her second husband, is a Harvard Law School graduate and had recently served as one of her attorneys.