Pauline Yvonne Parker was born on May 26, 1938, in Christchurch, New Zealand. She grew up in a working-class family. Her father, Herbert Rieper, and her mother, Honorah Mary Parker, worked as part-time house staff and gardeners for the University of Canterbury. Although they lived together, they were not married, which was a private matter that came to light later during a trial.

In her early teens, Pauline met Juliet Hulme. Both girls attended Christchurch Girls' High School. They both faced health challenges as children; Pauline suffered from osteomyelitis, while Juliet had tuberculosis. This shared experience helped establish a bond between them.

As their friendship grew, they created a rich fantasy world. They wrote plays and stories set in this imagined universe. Their intense friendship raised concerns among Pauline’s parents, who worried that their close relationship might be sexual. They were both accepted at each other's homes, with Pauline often staying overnight at Juliet's house.

The girls developed their own belief system. They rejected traditional Christianity and created a personal religion with their own saints and ideas about morality. They called their version of Heaven "The Fourth World," where they believed they could achieve moments of spiritual enlightenment.

In the summer of 1953, Pauline was not invited to stay with the Hulmes as she had been in previous years. By 1954, changes in Juliet's family began to create tension. Juliet's parents were separating, and her father lost his job at the university. They planned to move back to England, but Juliet was instead sent to stay with relatives in South Africa.

Facing separation, both girls were upset and decided that Pauline should join Juliet in South Africa. However, they knew both of their families might not approve.

On 22 June 1954, Pauline Parker and Juliet Hulme carried out a meticulously premeditated murder in Victoria Park, Christchurch. That afternoon, they had tea with Honorah Mary Rieper (Pauline’s mother) at a small kiosk in the park. After tea, the girls invited her for a walk along a secluded path, ostensibly for a pleasant outing. They had brought with them a brick concealed in a stocking — the weapon they intended to use. Roughly 130 meters down the forest trail, the girls attacked Honorah from behind. They bludgeoned her with the brick in a stocking, striking her at least 20 times. 

After the murder, Parker and Hulme ran back to the tea kiosk. When they reached the kiosk, they told the owners that Rieper had fallen and hit her head. However, Honorah's body was soon discovered in the park by one of the tea shop owners. Authorities found severe injuries on her head, neck, and face. The police also uncovered the murder weapon nearby in the woods. The story that Parker and Hulme had told about Rieper's accidental death did not hold up under investigation.

Parker, who was known as Pauline Rieper before the trial, and Hulme faced a sensational trial that attracted much public attention. During the trial, both girls were frequently discussed in the context of their sexuality and mental state. They were found guilty of murder on August 28, 1954. Because they were both underage, neither was eligible for the death penalty, and each received a five-year prison sentence.

Following their release, Parker was given a new identity and moved to New Zealand before leaving for England. In her later years, she lived in a small village in Kent and operated a children's riding school. She became a devout Roman Catholic and expressed remorse for her actions through a statement released by her sister.