Amy E. Duggan was born on October 31, 1873, in Milton, Connecticut, to James Duggan and Mary Kennedy. She was the eighth of ten children. She attended the Milton School and the New Britain Normal School, graduating in 1890.

In 1897, Amy Duggan married James Archer. They had a daughter, Mary J. Archer, born in December 1897. In 1901, the Archers were hired as caretakers for John Seymour, an elderly widower, and moved into his home in Newington, Connecticut. After Seymour's death in 1904, his heirs converted the residence into a boarding house for the elderly, with the Archers continuing to provide care for a fee and paying rent to Seymour's family. They operated the boarding house as Sister Amy's Nursing Home for the Elderly.

In 1907, Seymour's heirs decided to sell the house. The Archers relocated to Windsor, Connecticut, and purchased a home on Prospect Street, converting it into the Archer Home for the Elderly and Infirm. James Archer died in 1910 from what was officially deemed Bright's disease, a term for kidney diseases. Amy had taken out an insurance policy on him just weeks before his death, which allowed her to continue operating the Archer Home.

In 1913, Amy married Michael W. Gilligan, a widower with four adult sons. Gilligan, reportedly wealthy and interested in investing in the Archer Home, died on February 20, 1914, just three months after their marriage. The official cause of death was "acute bilious attack," or severe indigestion. Amy inherited his entire estate through a will that was later found to be a forgery, written in Amy Archer-Gilligan's handwriting.

Between 1907 and 1917, there were 60 deaths at the Archer Home. Relatives of the residents grew suspicious due to the unusually high number of deaths. Only 12 residents died between 1907 and 1910, but the number surged to 48 between 1911 and 1916. Among the deceased was Franklin R. Andrews, a seemingly healthy man who suddenly fell ill on the morning of May 29, 1914, while gardening at the Archer house and died by evening. The official cause of death was gastric ulcer.

After Andrews' siblings, including Nellie Pierce, found letters from their brother mentioning Amy Archer-Gilligan's requests for money, they noticed a pattern: clients often died soon after giving Amy large sums of money

As the deaths continued, Nellie Pierce reported her suspicions to the local district attorney, who largely ignored her. She then took her story to the Hartford Courant, which published the first of several articles on the "Murder Factory" on May 9, 1916. A serious police investigation followed, lasting almost a year.

The bodies of Gilligan, Andrews, and three other boarders were exhumed, revealing they had died from poisoning by arsenic or strychnine. Local merchants testified that Amy had been purchasing large quantities of arsenic, supposedly to kill rats. An examination of Gilligan's will revealed it was a forgery by Amy.

M. William Phelps, author of The Devil's Rooming House, noted that while Amy claimed to be buying arsenic to kill rats, she did not purchase all the arsenic that killed her patients. Some purchases were made by the doctor and patients themselves. The investigation initially focused on Dr. King, but attention returned to Amy when a thorough check of arsenic purchase records implicated her. Evidence showed Amy sending her patients to buy arsenic, leading to her arrest and conviction.

Archer-Gilligan was arrested and initially tried for five counts of murder, but her lawyer reduced it to a single count—the murder of Franklin R. Andrews. On June 18, 1917, she was found guilty and sentenced to death. She appealed and was granted a new trial in 1919, where she pleaded insanity. Her daughter, Mary Archer, testified that her mother was addicted to morphine. This time, Archer-Gilligan was found guilty of murder but was sentenced to life imprisonment.

In 1924, Archer-Gilligan was declared temporarily insane and transferred to the Connecticut Hospital for the Insane in Middletown, where she remained until her death on April 23, 1962.