Ruth Ellis was born as Ruth Neilson on October 9, 1926, in Rhyl, Denbighshire, Wales. She was the fifth of six children in her family. When Ruth was young, her family moved to Basingstoke, Hampshire, England. Her mother, Elisaberta "Bertha" Goethals, was a Belgian war refugee. Her father, Arthur Hornby, was a cellist from Manchester who played on Atlantic liners and later changed his surname to Neilson.

Ruth's early life was shaped by family tragedy. Her father's twin brother, Charles, died in 1928 when Ruth was just two years old. After this event, Arthur began to abuse Ruth's older sister, Muriel. Bertha, despite knowing about the abuse, did not intervene. Muriel became pregnant at the age of 14 due to the abuse, which led to a son being raised alongside her siblings. As Ruth reached her teenage years, her father turned his attention to her, but she resisted his attempts at abuse.

Ruth attended Fairfields Senior Girls' School in Basingstoke for a short while before leaving school at the age of 14. She then got her first job as an usherette at a cinema in Reading. After some time, Arthur moved to London for a new job, leaving his family behind. In 1941, Ruth made a new friend named Edna Turvey, who introduced her to a more lavish lifestyle. Edna and Ruth eventually moved in with Arthur in London, where the abuse continued.

At 17, in 1944, Ruth became pregnant by Clare Andrea McCallum, a married Canadian soldier. She had to leave to give birth at a nursing hospital. After giving birth to her son, whom she named Clare Andrea (Andy) Neilson, Ruth worked in various factory and clerical jobs to support him.

By the late 1940s, Ruth transitioned into a nightclub hostess in Hampstead and even became a nude model, which paid better than her previous jobs. In November 1950, she married George Johnston Ellis, a divorced dentist. Their marriage was troubled by George's violent behavior and alcohol abuse. Ruth became pregnant during the marriage but later gave birth to a daughter named Georgina. Their relationship ended soon after due to George's refusal to acknowledge paternity, and they divorced.

On Easter Sunday, April 10, 1955, Ruth Ellis took a taxi to the Hampstead area of London. She was looking for her lover, David Blakely. When she arrived at a flat where she suspected he might be, she saw him leave in his car. She paid off the taxi and walked to The Magdala pub, where she found Blakely's car parked outside.

Later that evening, around 9:30 PM, Blakely and his friend emerged from the pub. As Blakely searched for his car keys, Ruth took a .38 caliber Smith & Wesson revolver from her handbag. She fired five shots at Blakely. The first shot missed. As he tried to escape, she shot him again, causing him to collapse on the pavement. She stood over him and fired three more shots, one of which was fired just inches from his back.

Ruth struggled to fire a sixth shot. Eventually, she fired it into the ground, which caused a bullet to ricochet and hit a bystander named Gladys Yule. Gladys lost the use of her right thumb as a result.

After the shooting, Ruth asked Blakely's friend, Clive Gunnell, to call the police. An off-duty policeman heard her say, “I am guilty, I'm a little confused." Ruth was arrested immediately. Blakely was taken to the hospital but was pronounced dead due to multiple gunshot wounds.

At the police station, Ruth appeared calm and did not seem under the influence of any substances. She was taken to a magistrates’ court the following day and held on remand. Multiple examinations determined that there was no evidence of mental illness. On June 20, 1955, she was tried at the Old Bailey and was convicted of murder. The jury took only twenty minutes to reach a guilty verdict.

Ruth was sentenced to death and sent to Holloway Prison while she awaited execution. Despite her mother’s wishes for a petition for clemency, she initially did not want one. However, her solicitor later submitted a request for a reprieve, which was denied. After a final meeting with her lawyers, Ruth disclosed that Desmond Cussen, her former partner, had given her the gun and driven her to the murder scene.

On July 12, 1955, the day before her execution, she wrote a final letter to Blakely's parents expressing her love for their son. The next day, she was hanged in her prison cell at Holloway at around 9:00 AM. Following her execution, her remains were buried in an unmarked grave within the prison compound. Later, they were exhumed and reburied in a churchyard, with a headstone that read "Ruth Hornby 1926–1955." Ruth Ellis is remembered as the last woman to be executed in the United Kingdom.