Katherine Mary Knight was born on October 24, 1955, in Tenterfield, New South Wales, Australia. She grew up in a challenging family environment. Her mother, Barbara Roughan, was married to John "Jack" Roughan, with whom she had four sons. However, Barbara began an affair with Kenneth "Ken" Charles Knight, who worked with Jack. Because of local gossip and backlash, Barbara and Ken moved to Moree. None of Barbara's sons went with her; some stayed with their father while others were sent to live with an aunt in Sydney.

Barbara had four more children with Ken, including twin daughters who were born in 1955. Katherine was one of these twins. When Katherine was four years old, Jack Roughan passed away. Following this, Jack's two older sons moved in with Barbara and Ken. Ken had a drinking problem and was known to be violent. He abused Barbara regularly. Barbara often shared graphic details about her own relationships with her daughters, making them uncomfortable. Katherine reported that she experienced sexual abuse from some family members until the age of 11. Although some family members disputed these claims, many psychiatrists accepted Katherine's accounts as true.

Katherine's family had some Indigenous Australian heritage, which Barbara kept secret due to the racism in the area. In the family, Katherine was closest to her uncle Oscar Knight, who was a well-known horseman. She felt a deep sense of loss when he died by suicide in 1969. That same year, the family moved back to Aberdeen.

During her time at Muswellbrook High School, Katherine was known as a loner and often bullied smaller students. She had a reputation for being aggressive and once injured a boy with a weapon. Nevertheless, she was also recognized as a model student and received awards for her good behavior when she was not angry. After leaving school at 15, Katherine had not learned to read or write. She quickly found work in a clothing factory.

A year later, she left that job to work at a local abattoir, which she described as her "dream job." She became a cutter and was soon promoted to boning. She was given her own set of butcher knives. Katherine developed a habit of hanging her knives over her bed to keep them within reach, a practice she maintained throughout her life. People in the town remembered her as someone who would physically threaten anyone who offended her.

In 1973, Katherine met David Kellett, a co-worker at the abattoir. David struggled with heavy drinking due to past traumatic experiences. They married in 1974, but the marriage was tumultuous and violent. Knight showed aggressive behavior and had trouble managing her emotions. After their first child was born, the couple faced many challenges, leading to David eventually leaving Katherine.

In February 2000, Katherine Knight had a series of violent confrontations with her partner, John Price. After one such incident where Knight stabbed Price in the chest, he decided to end the relationship and kicked her out of his house. On February 28, Price sought a restraining order against Knight to protect himself and his children. That same day, he expressed to his co-workers that he feared Knight would kill him if he returned home. He felt trapped, stating he believed Knight might harm his children if he did not.

After Price returned home, he found that Knight had sent his children away. That night, he spent time with neighbors before going to bed. Meanwhile, Knight bought new lingerie and filmed her children, making unsettling comments. She later went to Price's house while he was asleep and watched television before taking a shower. After waking Price, they engaged in sexual activity, and then he fell asleep again.

The next morning, a neighbor grew worried when Price's car was still in the driveway. When he failed to show up for work, his employer sent someone to check on him. The neighbor and the worker knocked on Price’s window but then called the police after noticing blood on the front door. When officers arrived and broke down the door, they found Price's body inside and Knight in a comatose state from taking pills.

Knight had stabbed Price with a butcher's knife while he was sleeping. Evidence showed that he woke up, tried to turn on the light, and attempted to escape while Knight chased him. He got outside but either fell back inside or was pulled back, ultimately bleeding out.

Later, Knight went to an ATM and withdrew $1,000 from Price's account. His autopsy revealed he had been stabbed at least 37 times. After Price's death, Knight skinned him and hung the skin from a meat hook in the living room. She decapitated him and cooked parts of his body, preparing to serve the meat to his children. She set the table with dishes that included vegetables and left notes beside each plate marked with the names of Price's children.

A pot containing Price's head and vegetables was found still warm, indicating that the cooking had recently occurred. Knight also posed Price's body in an unusual way and left a note that contained disturbing messages, making unfounded accusations.

On March 2, 2001, Knight was charged with murder. Initially, she offered to plead guilty to manslaughter, but this was rejected. During her trial, she eventually changed her plea to guilty, but she continued to deny full responsibility for her actions. Psychiatrists noted she might have suffered from a mental disorder but concluded she was sane.

Knight was sentenced to life imprisonment without the possibility of parole. This marked the first time such a sentence was imposed on a woman in Australia. In June 2006, she appealed the life sentence, asserting it was too harsh, but her appeal was dismissed by the courts.

While serving her sentence at Silverwater Women’s Correctional Centre, Knight reportedly took on a leadership role among the prisoners and did not have a record of violence while incarcerated.