Susan McAllister was born in 1893 in Scotland into a life of poverty. She married John McLeod, who was killed during World War I, leaving her a widow with a daughter named Janet McLeod. In 1922, Susan remarried John Newell, an ex-serviceman employed as a Glasgow subway worker. The family resided in a rented room on Newlands Street, Coatbridge. Their marriage was tumultuous, marked by frequent arguments and instances of domestic violence. At one point, Susan assaulted John, leading him to report the incident to the police. However, no action was taken, and John subsequently left her, exacerbating her financial and emotional distress. ​

On June 20, 1923, 13-year-old newspaper boy John Johnston was selling papers in Coatbridge. He knocked on Susan Newell's door around 6:45 PM and was invited inside. An argument ensued over payment for a newspaper, during which Susan strangled John to death. Upon returning home and discovering the body, Susan's daughter Janet was coerced into assisting her mother in disposing of it. ​

The following morning, Susan and Janet placed John's body on a go-cart, concealed under a quilt, and began transporting it toward Glasgow. A lorry driver offered them a ride, dropping them off on Duke Street in Glasgow. Their suspicious behavior attracted the attention of local residents, leading to police intervention. Susan attempted to flee but was apprehended, and John's body was discovered in the cart. ​

Both Susan and her husband John were charged with murder and stood trial in September 1923. John Newell provided a solid alibi and was acquitted. Susan's defense pleaded insanity, which was rejected by the jury. After deliberating for 35 minutes, the jury found her guilty, with a recommendation for mercy. Nevertheless, she was sentenced to death. ​

Efforts to secure a reprieve, including a petition highlighting her destitution and abandonment by her husband, were unsuccessful. Susan Newell was executed by hanging on October 10, 1923, at Duke Street Prison in Glasgow, becoming the last woman to be executed in Scotland. ​