Catherine Mandeville was born around 1793 in Harbour Grace, Conception Bay, Newfoundland. She later moved to Salmon Cove near Port de Grave, where she entered into a tumultuous marriage with John William Snow, a planter and fisherman. The couple had seven children and officially married on October 30, 1828. Their relationship was marked by frequent and violent altercations, with neighbors often overhearing their disputes. Catherine was known to defend herself during these confrontations, an uncommon stance for women of that era. John Snow was reputed to be abusive towards both his wife and their servants. At the time, under English common law, women had limited rights and were often considered the property of their husbands, a factor that would later influence Catherine's trial. ​

On the night of August 31, 1833, John Snow vanished without a trace. Subsequent investigations led by Magistrate Robert Pinsent uncovered dried blood on Snow's fishing stage, raising suspicions of foul play. Attention turned to Arthur Spring, an indentured servant, and Tobias Mandeville, Catherine's cousin and alleged lover. Spring eventually confessed that, at Catherine's behest, Mandeville shot John Snow, and together they disposed of his body by anchoring it with a grapnel and casting it into the sea. Catherine fled but later surrendered to authorities. Despite the absence of direct evidence linking her to the murder, she was arrested and charged.

The trial commenced on January 10, 1834, in St. John's. All three defendants pleaded not guilty. The prosecution acknowledged the lack of direct evidence against Catherine but presented a chain of circumstantial evidence suggesting her involvement. After a 12-hour deliberation, the jury found all three guilty. Catherine was sentenced to death by hanging. However, she claimed to be pregnant, and a jury of matrons confirmed her condition. Her execution was postponed until after the birth and nursing of her child, Richard Snow.

On July 21, 1834, Catherine Snow was executed in St. John's, making her the last woman to be hanged in Newfoundland. She maintained her innocence until the end. Her case has since been the subject of debate, with many questioning the fairness of her trial and the validity of the evidence presented against her. In 2012, a mock retrial was held, resulting in a modern jury acquitting her, highlighting the enduring controversy surrounding her conviction.