Phoebe McWain was born around 1847 in Ontario, Canada. On January 16, 1867, she married George Campbell in Perth, Ontario. The couple settled in a log cabin in Thorndale, Middlesex County, Ontario. Little is documented about Phoebe's early life before her marriage.

On the morning of July 15, 1871, George Campbell was brutally murdered in his home. Initially, Phoebe claimed that two masked intruders had broken into their cabin, attempting to rob them and ultimately killing George when he resisted. However, inconsistencies in her account and her unemotional demeanor during George's funeral aroused suspicion.

Investigations led to the arrest of several local men, including Thomas Coyle, a farmhand employed by George. Doubts about Phoebe's innocence grew when witnesses reported seeing her conversing with Coyle shortly before the murder. Further scrutiny revealed that Phoebe had made contradictory statements about the events of that morning.

During her trial, which commenced on April 1, 1872, Phoebe accused George of infidelity, alleging an affair with her cousin's wife. The prosecution presented a letter in which Phoebe wrote, "I never shall say you done any such thing again—if I have to die for it." When questioned about her changing testimony, Phoebe claimed that George's ghost had appeared to her, declaring both her and Coyle innocent. The jury deliberated for just an hour before returning a guilty verdict. Phoebe was sentenced to death and was executed by hanging on June 20, 1872, at the age of 25.