Sidney Harry Fox was born in 1899 in Norfolk, England, to Rosaline Rallison and William George Fox, a railway porter. He was the youngest of four children, though some accounts suggest he may have been illegitimate, as his father reportedly left the family when Sidney was very young.

From an early age, Fox exhibited a penchant for deceit and petty crime. As a teenager, he worked in various domestic service positions but was dismissed for theft. His early criminal activities included forging cheques, which led to his first arrest in 1916. To avoid prosecution, he enlisted in the Royal Air Force by falsely claiming to be an Old Etonian, but continued his fraudulent activities, resulting in a three-month prison sentence.

Throughout the 1920s, Fox and his mother led a transient lifestyle, moving from town to town and engaging in various scams to support themselves. Fox often posed as a gentleman to defraud wealthy individuals, while his mother was complicit in his schemes. 

On October 23, 1929, Sidney Fox and his mother, Rosaline, checked into the Hotel Metropole in Margate, England. That evening, a fire broke out in their room. Fox raised the alarm, claiming his mother was trapped inside. Despite efforts to save her, Rosaline was found dead, and the fire was extinguished.

Initially, Rosaline's death was attributed to the fire. However, forensic pathologist Sir Bernard Spilsbury conducted a post-mortem examination and concluded that she had been strangled before the fire was set. This finding led to Fox's arrest and subsequent trial for murder.

During the trial at the Sussex Assizes in March 1930, the prosecution presented evidence of Fox's financial motives, including a recently taken out life insurance policy on his mother. The jury found him guilty, and he was sentenced to death. Fox was executed by hanging at Maidstone Prison on April 8, 1930.

In recent years, some have questioned the safety of Fox's conviction. A 2021 episode of the BBC series "Murder, Mystery and My Family" suggested that Rosaline's death may have been due to natural causes and that the fire was accidental, casting doubt on the forensic evidence used to convict Fox.