She was born Honora Kelley in Boston's North End in the mid-1850s, to Irish immigrant parents. Her mother died of consumption and her father, a tailor known locally as Kelley the Crack, was committed after he was found in his shop sewing his own eyelids shut. She and a sister were left at the Boston Female Asylum and she was placed as an indentured servant with a family in Lowell named Toppan, whose name she took, along with the given name Jane. She was never adopted and never inherited.
She trained as a nurse at Cambridge Hospital in 1885 and later at Massachusetts General. She was liked, called Jolly Jane, and she was already killing. She altered patients' morphine and atropine doses, sometimes to kill and sometimes to bring them to the edge and back, and falsified their charts. She later described climbing into bed with them as they died and holding them. Morphine constricts the pupils and atropine dilates them, and she used the two together partly because the combination masks the signs a physician would look for. She was dismissed from both hospitals over irregularities without a criminal accusation, and moved into private nursing, which put her inside families.
In 1901 she was engaged by the Davis family of Cataumet on Cape Cod, whose matriarch, Mattie Davis, had come to Boston to collect an unpaid debt from her. Mattie Davis died at Toppan's lodgings. Toppan travelled to Cataumet to help, and over the following six weeks Mattie's husband Alden and both their daughters, Annie Gordon and Mary Gibbs, also died. A surviving son-in-law demanded a toxicological examination of Mary Gibbs, and the arsenic-free but opiate-laden result led to exhumations and to her arrest in Amherst, New Hampshire, on October 29, 1901.
She confessed to thirty-one murders and said she wanted to have killed more people than any man or woman who had ever lived. Her lawyer ran insanity, two of her half-siblings having been institutionalised, and in June 1902, after a trial lasting a day, the jury found her not guilty by reason of insanity in under half an hour.
She was committed to the Taunton Insane Hospital for life. She is said to have spent her early years there refusing food she thought was poisoned. She died on August 17, 1938, aged about eighty-four. Only three deaths were formally charged. The thirty-one is her own count, and most historians of the case regard it as plausible and possibly low.