Jean Lee was born as Marjorie Jean Maude Wright on December 10, 1919, in Dubbo, New South Wales. She was the youngest child of Charles Wright and Florence Peacock. Her father worked for the railway, and the family was considered highly respectable. In 1927, they moved to Sydney, settling in the suburb of Chatswood. Marjorie attended Chatswood Public School and later went to a convent school in North Sydney. She finished her education at Willoughby Central Domestic High School, where she learned shorthand and typing.

After school, Marjorie's first job was as an office junior at a motor company in Chatswood. Over time, she worked in various capacities, including as a milliner, stenographer, and laborer in a canned-goods factory. In March 1938, Marjorie married Raymond Brees, a house painter seven years older than her. They had known each other since childhood. However, their marriage faced challenges due to financial issues, as Brees struggled to find regular work and had problems with alcohol.

Marjorie gave birth to a daughter a few months after their marriage. In July 1939, Brees was convicted of auto theft and received a suspended sentence. When World War II began, Brees enlisted and served in the military. During their separation between 1942 and 1943, Marjorie found it difficult to care for herself and her daughter. Eventually, she left her daughter in the care of her mother while she sought work in Brisbane, where she found a job as a waitress.

In late 1943, Marjorie met Morris Dias, a man involved in petty crime. They moved together to different cities, including Sydney and Adelaide, before settling in Perth. While living with Dias, Marjorie began drinking and faced violence in their relationship. To support Dias, she started working as a prostitute when he was arrested for outstanding charges.

Marjorie, known by several aliases including "Jean Lee," continued in this line of work in Sydney, gaining many convictions for prostitution. In 1946, after ending her relationship with Dias, she returned to Sydney and began working as a barmaid while also returning to prostitution. It was during this period that she met Robert Clayton, and the two formed a complicated relationship.

On November 7, 1949, Jean Lee and her accomplices, Robert Clayton and Norman Andrews, met William 'Pop' Kent at the University Hotel in Carlton, Melbourne. Kent was a 73-year-old SP bookmaker. After some drinks together, he invited the trio back to his boarding house for more alcohol. Once they arrived at Kent's room, the atmosphere turned from friendly to dangerous.

Lee attempted to seduce Kent to gain access to his money. When her first attempts failed, she became frustrated. In a fit of anger, she grabbed a wine bottle and struck Kent on the head, breaking the bottle. She then picked up a broken chair leg and began hitting him. Hearing the commotion, Clayton and Andrews returned to the room, where they assisted Lee in binding Kent's hands and feet.

The three then tortured Kent, demanding to know where he kept more money. They inflicted serious injuries on him, including slashing his face and burning him with cigarettes. Despite Kent pleading for mercy, they continued their attack. After a while, Kent became unresponsive, and ultimately died as a result of their violence.

After the murder, the trio searched the room for valuables. When they found nothing worth taking, they left the boarding house as if nothing had happened. Soon after, neighbors grew suspicious due to the lack of noise and called the police to investigate. The police found Kent’s body and started looking for Lee and her accomplices.

Later that night, the three were arrested at their hotel. Lee initially refused to speak but later claimed full responsibility for the killing, saying she acted alone. However, all three were charged with murder and faced trial. The court heard evidence of their actions that night, leading to their conviction.

On March 25, 1950, the jury found Lee, Clayton, and Andrews guilty of murder. They were sentenced to death. The legal battles continued for several months, including an appeal that ultimately upheld their sentences.

On February 19, 1951, Jean Lee was executed by hanging at Pentridge Prison, becoming the last woman executed in Australia. Clayton and Andrews were executed shortly after her. Their bodies were buried in a graveyard reserved for executed prisoners.