John Leslie Coombes was born on September 14, 1954, in Victoria, Australia. Little has been publicly documented about his early life, upbringing, or psychological profile before he committed his first known murder.

In 1984, John Leslie Coombes committed his first murder by stabbing Henry Desmond Kells, a 44-year-old man, at Kells' home in Chelsea. Coombes was sentenced to life imprisonment in December 1985, but his sentence was later reduced to a minimum of 11 years.

Seven weeks after his release in 1996, Coombes was charged with the murder of Michael Peter Speirani. Speirani had gone missing while on a fishing trip. His body was found stabbed and mutilated, dumped a few kilometers off the coast of Port Phillip Bay. In 1998, Coombes received a 10-year minimum sentence for this crime. He was paroled in 2007.

In August 2009, he strangled 27-year-old Raechel Betts, a childcare worker, at the Phillip Island home of his then-girlfriend and co-defendant Nicole Godfrey. Following the murder, he mutilated her body in a bathtub, dismembered the remains, and disposed of them by throwing them from a pier in Newhaven, Victoria.

Coombes changed his plea to guilty during pre-trial proceedings at the Supreme Court of Victoria. In August 2010, he was sentenced to life imprisonment without the possibility of parole. Justice Geoffrey Nettle emphasized the pattern in Coombes’ killings, stating that the offender demonstrated "a frightening predilection for homicide" and was highly likely to kill again if ever released.

Since then, Coombes has remained in prison.