Lucy Letby was born on January 4, 1990, in Hereford, Herefordshire, England. She was the only child of a finance manager and an accounts clerk. Letby grew up in a household where education was valued. She attended Aylestone School and later, Hereford Sixth Form College. According to a friend from secondary school, Letby's birth was difficult, and she was grateful to the nurses who helped during that time. This gratitude inspired her to want to become a nurse one day.

After finishing school, Letby pursued nursing at the University of Chester. During her three years of training, she worked as a student nurse and completed placements at two hospitals: Liverpool Women's Hospital and the Countess of Chester Hospital. She was the first in her family to attend university. Letby graduated in September 2011.

In 2012, after completing her education, Letby began working as a registered nurse in the neonatal unit of the Countess of Chester Hospital. In a staff profile published in 2013, she talked about her responsibilities for caring for vulnerable babies and supporting their families. Letby showed a keen interest in her work, although she later mentioned that non-intensive care work did not hold her interest as much.

Throughout her career, she participated in efforts to raise funds for her unit, as she wanted to improve the care provided. She had multiple training placements, including stints at Liverpool Women's Hospital in late 2012 and early 2015. In 2015, she qualified to work with infants in intensive care. By April 2016, Letby was moved from night shifts to day shifts.

However, in June 2016, concerns about her conduct began to surface among hospital consultants. They requested her removal from clinical duties for further investigation into various incidents that had occurred while she was on duty. Letby was subsequently transferred to roles with less direct patient care. She continued to work until her arrest in 2018.

In June 2015, the neonatal unit at Countess of Chester Hospital experienced a troubling increase in infant collapses, with four incidents occurring in rapid succession. Three of these resulted in deaths. Typically, the unit saw only two or three deaths in a year, and the infants involved failed to respond normally to resuscitation. Lucy Letby, a nurse, was present during all the incidents. Initial reviews deemed the deaths as medication errors, and at first, concerns were not linked directly to her.

As the year progressed, a ward manager also conducted her review and noted that Letby was the only staff member consistently present during these unexplained incidents. Medical consultants grew increasingly alarmed and expressed their concerns to management. In February 2016, an investigation by the lead neonatologist determined that Letby was the common factor in five unexplained deaths and collapses. This prompted a request for immediate action, but the hospital executives deemed the occurrences coincidental.

Yet, the mortality rate among the infants under Letby's care remained unusually high. Reports indicated a 10% increase in neonatal deaths at the hospital compared to previous years. Despite a rising number of unexplained deaths, Letby continued to be assigned to the unit.

In late June 2016, after two triplet babies died on consecutive days, there was renewed urgency to remove Letby from duty, but hospital management resisted calls for her removal, insisting she was safe to work. By this time, police involvement was being discussed due to the increasing number of deaths, leading to a formal investigation.

Lucy Letby was finally arrested in July 2018, suspected of eight counts of murder and six counts of attempted murder. She was charged in November 2020. The trial began in October 2022, with Letby pleading not guilty. Evidence presented during the trial included testimonies from families of victims, revealing distressing incidents. For instance, one mother testified to finding her baby with blood around his mouth while Letby was present.

The prosecution argued that Letby exhibited suspicious behavior, such as sending texts to friends during alarming incidents and searching for victim families online. Furthermore, hospital records and other evidence suggested that she had falsified details regarding incidents to cover her tracks.

On August 18, 2023, Letby was found guilty of murdering seven infants and attempted to murder six others. The methods she employed included injecting the babies with air and poisoning them with insulin. She received a whole life order, making her one of the most notorious serial killers in recent British history, and she is currently serving her sentence.