Ivan Milat was born on December 27, 1944, at Crown Street Women's Hospital in Guildford, New South Wales. He was the son of Stjepan Marko "Steven" Milat, a Croatian emigrant and laborer, and Margaret Elizabeth Piddleston, an Australian. Ivan was the fifth of their fourteen children.

The Milat family was very poor and initially lived on a farm in Bossley Park, west of Sydney, before moving to Liverpool. Despite their tough circumstances, Ivan’s parents worked hard to raise and educate their children, sending them to Catholic schools. However, Ivan's father was known to have a bad temper, likely worsened by his alcoholism. The ten Milat boys often got into trouble and were familiar with using knives and guns, spending their time shooting at targets in their yard.

From a young age, Ivan showed signs of antisocial and violent behavior. His siblings remembered him attacking animals with machetes, which led to him being sent to a residential school at age 13. By 17, he was in juvenile detention for theft, and at 19, he broke into a shop. In 1964, he was sentenced to 18 months for breaking and entering, and shortly after his release, he was caught driving a stolen car, earning a two-year hard labor sentence. In 1967, at age 22, he received a three-year sentence for theft.

On April 7, 1971, Milat abducted two 18-year-old female hitchhikers near Liverpool railway station, threatening them with a knife. He raped one of the girls before they managed to escape at a petrol station café. Milat was arrested the same day and charged with rape and armed robbery. While waiting for his trial, he committed several robberies with his brothers and faked his suicide by leaving his shoes at The Gap, a known suicide spot in Sydney.

Authorities believe Milat fled to Queensland and Victoria and then to New Zealand, where he stayed for two years. It is suspected that he returned to Australia using a fake passport and lived interstate to avoid being caught. In 1974, he was arrested again when his mother was hospitalized for a heart attack, but the charges against him were dropped with the help of the family lawyer, John Marsden.

In 1975, Milat got a job as a truck driver and worked off and on for the Roads & Traffic Authority for about 20 years until his arrest. In 1977, he tried to rape and murder two female hitchhikers traveling from Liverpool to Canberra, but he was never charged for these crimes.

On September 19, 1992, two runners discovered a hidden body while orienteering in Belanglo Forest. The next morning, police found a second body nearby. These were confirmed to be Clarke and Walters through dental records. Walters had been stabbed fifteen times, including in the chest, neck, and back, paralyzing her. Clarke had been shot ten times in the head, likely used as target practice. After searching the forest, police believed there were no more bodies.

On October 5, 1993, a local man found bones in a remote part of Belanglo. Police discovered two bodies identified as Gibson and Everist. Gibson had been stabbed eight times and paralyzed by a cut to his spine. Everist had been beaten, with a fractured skull and broken jaw, and stabbed once in the back. Gibson's camera and backpack had previously been found far from Belanglo, confusing investigators.

On November 1, 1993, police found a skeleton in Belanglo, later identified as Schmidl. She had at least eight stab wounds, some severing her spine. Clothes found near her body matched another missing backpacker, Habschied. On November 4, 1993, Habschied and Neugebauer's bodies were found in shallow graves nearby. Habschied had been decapitated, and Neugebauer was shot six times in the head. Some victims did not die instantly from their injuries.

The investigation revealed evidence of torture among the victims. In response, Task Force Air was set up on October 14, 1993, by the New South Wales Police, including over twenty detectives and analysts. On November 5, the government increased the reward for information to A$500,000. Using advanced technology, investigators narrowed their suspect list from 230 to 32. Some speculated multiple killers were involved due to the different methods and separate burials.

On November 13, 1993, Paul Onions in the UK contacted police. He had been backpacking in Australia on January 25, 1990, when a man named "Bill" attempted to rob him near Belanglo. Onions escaped while Bill shot at him and later described the incident to police. This lead was rediscovered on April 13, 1994, and Onions' account was corroborated by others.

Police began surveillance of Ivan Milat's house on February 26, 1994. They learned Milat had recently sold his silver Nissan Patrol, and he had not been working on the days of the attacks. Acquaintances described his obsession with weapons. Onions flew to Australia and identified Milat as his assailant on May 5, 1994.

Milat was arrested on May 22, 1994, at his house. A search revealed weapons matching those used in the murders and items belonging to the victims. Police also searched properties of Milat's relatives, finding more items linked to the victims. Milat was initially charged with robbery and weapons offenses and, on May 31, was charged with the seven backpacker murders. His trial began on March 26, 1996, with overwhelming evidence against him.

On July 27, 1996, after eighteen weeks of testimony, a jury found Milat guilty of the murders. He received a life sentence without parole for each count and additional sentences for the attempted murder, false imprisonment, and robbery of Onions.

Ivan Milat died on October 27, 2019, from esophagus and stomach cancer while in prison. Despite numerous appeals and investigations into other possible victims, Milat maintained his innocence, although he had once admitted to his mother that he was responsible for the backpacker murders. Police believe Milat may have committed additional murders, given his history and modus operandi.