Mary Pearcey was born Mary Eleanor Wheeler on March 26, 1866, in Ightham, Kent, United Kingdom. There were many stories about her family, but some of them were not true. It was once said that her father, Thomas Wheeler, had been convicted of murder and hanged. However, author Sarah Beth Hopton found no evidence to support this claim and noted that the newspaper article that first mentioned it was later retracted.

As she grew up, Mary Wheeler took the surname Pearcey from John Charles Pearcey, a carpenter who she lived with for a time. Their relationship ended because he left her due to her infidelity. After that, Mary began living with a furniture remover named Frank Hogg. Frank had another lover named Phoebe Styles. Mary encouraged Frank to marry Phoebe when she became pregnant, leading them to settle in Kentish Town, London. Phoebe Styles gave birth to a daughter, and she was also named Phoebe Hogg.

On 24 October 1890, Mary Pearcey invited Phoebe Hogg to her home. Phoebe Hogg brought her eighteen-month-old baby. Later in the afternoon, neighbors reported hearing screaming and violent sounds. That evening, police found a woman's body on a pile of rubbish in Hampstead. Her skull had been crushed, and her head was almost severed from her body. A black perambulator was discovered about a mile away, stained with blood. The body of the child was also found in Finchley, appearing to have been smothered. Initially, the press speculated the adult victim was an "unfortunate," but she was later identified as Phoebe Hogg, and the toddler was identified as her daughter.

Witnesses reported seeing Pearcey pushing the baby’s pram through North London at night after the murders. The police conducted a search of her home, where they found blood spatter on various surfaces and items, including a skirt and an apron. They also discovered blood and hair on a fireplace poker and a carving knife. When questioned by officers, Pearcey claimed she had been trying to deal with a mouse problem. She was charged with murder and maintained her innocence during the trial, but she was convicted.

On 23 December 1890, Pearcey was executed by hanging. Executioner James Berry described her as the most composed person in the execution party. She made a final statement, claiming her sentence was just but that much of the evidence against her was false. Initially, she refused help from female prison staff but later agreed. Berry noted that her execution was quiet and painless.

Pearcey's case received significant media attention at the time. Madame Tussauds created a wax figure of her and displayed the pram used in the crime. The exhibit attracted large crowds. Additionally, her hanging noose is now displayed at the Crime Museum in New Scotland Yard. Some theories later suggested a possible link between Pearcey and the Jack the Ripper murders, although there was no physical evidence connecting her to those crimes.