Born and raised in Eau Claire, Wisconsin to George and Elsie Brunner, she moved to California upon graduating from the University of Wisconsin–Madison in 1965 and took up a job as library assistant at UC Berkeley. She met 33-year-old career criminal Charles Manson, who had been released from Terminal Island prison several weeks prior to their meeting. She let Manson stay at her apartment and, after a period of weeks, the two became lovers, Brunner quit her job, and the two began to drift around California in a van, meeting other young women.
During the summer of 1967, Manson impregnated Brunner. On April 15, 1968 she gave birth to a son she named Valentine Michael (nicknamed "Pooh Bear"; Valentine Michael Smith is the name of the protagonist in Robert Heinlein's 1961 novel Stranger In A Strange Land) in a condemned house in Topanga Canyon and was assisted during the birth by several of the young women from the Family. Brunner (like most members of the group) acquired a number of aliases and nicknames, including: "Marioche", "Och", "Mother Mary", "Mary Manson", "Linda Dee Manson" and "Christine Marie Euchts".
After arriving in Venice, California, Brunner and Manson met 18-year-old Lynette Fromme and the three began living together in a rented house at 636 Cole Street in San Francisco. Over the course of the following two years, the Family enlarged to include between 20 and 30 individuals living communally; some, like Brunner and Fromme, became ardent followers of Manson, while others drifted in and out of the group.
After traveling along the California coast and excursions to Washington, Oregon and Nevada, the ever-growing number of young women and men eventually settled down at Spahn Ranch, an occasional film set operated by an elderly man named George Spahn, near the Los Angeles suburb of Chatsworth. Manson ostensibly based his commune on principles of freedom and love, but he exerted dictatorial control. In addition to having sex with Spahn and others, the female followers were sent to the city on criminal activities such as fraud. Manson also had illegal firearms and played host to a motorcycle gang.
On April 21, 1968 Brunner and Family members Manson, Susan Atkins, Ella Jo Bailey, Dianne Elizabeth Lake, Nancy Laura Pitman, Bruce Vann Hall, Marcus John Arneson and Suzanne Scott were arrested near Little Sycamore Canyon, in southern Ventura County, California. They were found sprawled nude around a campfire beside a 1952 bus "stuck in a deep ditch", that had been reported stolen in San Francisco on April 12. Manson was remanded into custody under the suspicion of grand theft auto and possession of two driver licenses.
Scott, Atkins, Lake and Hall were charged with possessing fictitious and fraudulent driver's licenses. Pitman, Arneson and Bailey were jailed on charges of disorderly conduct and not possessing proper identification. Five other Family members were released without being charged. Brunner was booked on suspicion of endangering the life and health of a child, after her one-week-old son, Valentine was found by deputies improperly dressed and shivering. The baby was placed in the care of the Ventura County General Hospital.
Charges against Brunner were later reduced to contributing to the delinquency of a minor and she was given two years probation and a 15-day suspended jail sentence. She subsequently told authorities she planned to return to her parents' home in Wisconsin and Valentine was returned to her.
On July 25, 1969, 21-year-old Family member, musician and aspiring actor Bobby Beausoleil left Spahn Ranch, accompanied by Brunner and group member Susan Atkins to pay a visit to an associate named Gary Allen Hinman at his home in Topanga Canyon, just south of Malibu. Hinman had been friendly with the Family and had often allowed members to stay at his home. Both Beausoleil and Brunner had previously lived with Hinman for short periods of time and, according to a 1981 interview with Beausoleil, Brunner was close friends with Hinman. Beausoleil was in possession of a knife and a 9 mm Radom pistol that he had borrowed from Family member Bruce Davis.
On July 31, 1969, Hinman was found murdered in his home. His face had been deeply slashed on the left side and he had two stab wounds to the chest. Hinman's house had been ransacked and the words "Political Piggy" written and a paw print (intended to be symbolic of the Black Panther Party) drawn on the wall in his blood. Both of Hinman's vehicles were missing: a Volkswagen van and a Fiat station wagon. On August 5, 1969, Beausoleil was found by the California Highway Patrol asleep in the back of Hinman's Fiat near San Luis Obispo, California. Beausoleil had a sheath knife attached to his belt. Robert Kenneth "Bobby" Beausoleil was arrested and charged with the murder of Gary Allen Hinman.
On August 8, 1969, Brunner and another Family member, Sandra Good, were arrested in San Fernando, California at a Sears store for purchasing items with a stolen credit card. Brunner had signed for her purchases with the alias "Mary Vitasek" and the two women fled the store when a cashier became suspicious. After being followed by the store manager, the police caught up with the two and found them in possession of numerous stolen credit cards and fake identification cards. They were charged with violating Section 459 (burglary) and 484e (grand theft by fraudulent use of credit card) of the California Penal Code and booked into the Sybil Brand Institute Reception Center later that evening.
That same evening, Family members Charles "Tex" Watson, Susan Atkins, Linda Kasabian and Patricia Krenwinkel went to 10050 Cielo Drive and murdered pregnant actress Sharon Tate and her guests Wojciech Frykowski, Jay Sebring and Abigail Folger, as well as 18-year-old Steven Parent, who was visiting Tate's groundskeeper William Garretson.
There is agreement that Manson was behind the killing of Hinman. Brunner was present throughout and was the key witness for the prosecution. She testified at Beausoleil's trial that Beausoleil killed Hinman (a musician), because Hinman had refused to join Manson's pop group.
There have been many other suggestions. Vincent Bugliosi, who was the prosecutor in the Tate-LaBianca case, claimed in his book that Manson instructed Beausoleil, Brunner and Atkins to go to Hinman's house to get money and titles to Hinman's vehicles. This account was later corroborated by various Family members. However, Beausoleil denied Manson's direct involvement and disputed that neither Brunner nor Atkins had any direct knowledge of why he was visiting Hinman.
Beausoleil contended that he went to Hinman's home in order to confront Hinman and collect $1,000 from him. Beausoleil claimed that he had purchased from Hinman tabs of mescaline that he then sold to a biker gang called the Straight Satans. He further explained that that several hours after the gang purchased the mescaline from Beausoleil, they showed up at Spahn Ranch, claiming the mescaline was poisoned with strychnine, demanded their money back and threatened to kill Beausoleil.
Beausoleil contended that both Brunner and Atkins merely went along with him to Hinman's because they "liked" Hinman and wanted to visit. In the interview, he states that neither he nor Brunner nor Atkins were instructed by Manson to go to Hinman's and that he initially had no intention to kill him. This contradicted Beausoleil's own testimony at his first trial in 1969, when he claimed that Manson did in fact instruct him to kill Hinman. Beausoleil claimed "Mary Brunner was just scared to death. She just faded into the woodwork" during the murder, but that Atkins went back into the house after Beausoleil stabbed Hinman and placed a pillow over Hinman's face. He also contended that it was Atkins who wrote the words "Political Piggy" on Hinman's wall (at Beausoleil's instructions).
In October 1969, police raided the Family's new residence at Barker Ranch near Death Valley, California, holding most of the group in custody on charges of automobile theft. Among those arrested were Atkins, who, while being questioned by police sergeants Whitley and Guenther on October 13, 1969, implicated herself in the murder of Hinman and told the officers that Manson had sent her and Beausoleil to Hinman's residence to force Hinman to hand over money that Manson believed Hinman had inherited. Atkins also told the police that Beausoleil alone acted in the murder of Hinman, stabbing him twice in the heart after detaining him in his home for over two days. Atkins also maintained that it was Beausoleil who slashed Hinman's face, not Manson. However, Atkins gave several differing accounts of the murder of Hinman; at times claiming that she killed Hinman, Manson killed Hinman or that Beausoleil killed Hinman.
Mary Brunner and Susan Atkins were subsequently charged along with Bobby Beausoleil for the murder of Gary Hinman. Brunner later received immunity from prosecution to testify against both Beausoleil and Atkins. His first trial, which began in November 1969 ended in a hung jury, with Beausoleil claiming that Manson alone had murdered Hinman.
However, during Beausoleil's March 1970 trial, Brunner repudiated her testimony that Beausoleil murdered Hinman and Beausoleil produced an affidavit signed by Brunner stating that he did not stab Hinman. Called to the stand to testify, Brunner eventually repudiated her previous testimony and insisted that she had said Beausoleil stabbed Hinman to death in her attempt to absolve Charles Manson of any participation in the crime. Various former Family members such as Ella Jo Bailey contradicted this testimony and testified that Manson confessed to them that he in fact was present at the Hinman house and that he fully participated in the murder.
Beausoleil was sentenced to death, later commuted to life (See California v. Anderson); Atkins pleaded guilty for her participation in Hinman's death and was sentenced to life imprisonment. Bruce Davis was charged in the murder after it was learned Beausoleil had called Davis at Spahn Ranch and asked him to come over and pick up Hinman's Volkswagen van. Separate trials were held for the murders of Gary Hinman and Spahn Ranch worker Donald "Shorty" Shea, for Family members Davis, Charles Manson, and Steve "Clem" Grogan.
Brunner subsequently returned to the remaining members of the Family and rallied support for those incarcerated for the Tate/LaBianca murders. Her son was sent to live with her parents.
On August 21, 1971, Brunner, accompanied by Family member Catherine "Gypsy" Share and several male Family associates — Dennis Rice, Charles Lovett, Larry Bailey, and Kenneth Como — drove a white van to a Hawthorne, California Western Surplus Store. Once inside the store, the group brandished guns and ordered the store patrons and clerks to lie on the ground. They then took 143 rifles from the premises, loading them into their van, while a store clerk tripped the silent alarm. According to police officers, the group then debated whether to kill all of those in the store.
Police alleged the group's plan was to hijack a Boeing 747 and threaten to kill one passenger every hour until Manson and fellow Family members were released from prison. When a police squad car arrived, Share opened fire on the vehicle, shattering the windshield. As more squad cars arrived, they blocked the van from fleeing the scene, spraying it with over 50 bullets; the Family members fired nearly 20 rounds at the officers. When police finally gained control of the scene and apprehended the group, Mary Brunner, Catherine Share, and Larry Bailey were injured.
Brunner was convicted and received a sentence of 20 years to life, She was sent to the California Institution for Women, where Leslie Van Houten, Susan Atkins and Patricia Krenwinkel were serving their sentences for their participation in the Tate-LaBianca murders. Brunner disappeared from the public eye after being paroled in 1977.