Sarah Reynolds was born around 1819 in Potton, Bedfordshire, England, to Philip and Ann Reynolds. Her father, a barber, passed away when Sarah was seven, leading her mother to engage in several relationships thereafter. Described as tall with auburn hair and brown eyes, Sarah married Simeon Mead in 1838 at the age of 19. The couple resided in Potton before relocating to Tadlow in 1840, possibly due to Simeon's suspicions regarding Sarah's alleged infidelity. That same year, Sarah gave birth to their son, Jonah.​

In 1840, tragedy struck when Jonah died at seven months old under unclear circumstances. Shortly after, in October 1840, Simeon Mead also died unexpectedly. While suspicions arose, no formal investigations were conducted at the time.​

In 1841, Sarah married William Dazley, and they moved to Wrestlingworth. Their marriage was tumultuous, marked by William's heavy drinking and physical abuse towards Sarah. She confided in a friend, William Waldock, expressing a willingness to kill any man who struck her.​

By October 1842, William fell severely ill, exhibiting symptoms consistent with arsenic poisoning, including vomiting and severe stomach pains. Despite medical attention and initial signs of recovery, his condition deteriorated after consuming pills prepared by Sarah. He died on October 30, 1842. 

Following his death, Sarah became engaged to William Waldock, but local suspicions led to the exhumation and examination of William Dazley's body, revealing traces of arsenic. An arrest warrant was issued, prompting Sarah to flee to London, where she was subsequently apprehended.​

During the investigation, the bodies of Jonah and Simeon Mead were exhumed. Tests detected arsenic in Jonah's remains, but Simeon's body was too decomposed for conclusive results. Sarah was charged with the murder of William Dazley. Her trial commenced on July 22, 1843, at the Bedfordshire Summer Assizes. Witnesses, including chemists who sold her arsenic and individuals who observed her administering pills to William, testified against her. 

After a brief deliberation, the jury found her guilty. On August 5, 1843, Sarah Dazley was executed by hanging at Bedford Gaol before a crowd of thousands, earning her the moniker "The Potton Poisoner."​