He was sentenced to life imprisonment with a non-parole period of 35 years for ordering the murders of three people and conspiracy to murder a fourth (which was unsuccessful). On 19 April 2010, while incarcerated at Barwon Prison, Williams was beaten to death with the stem of an exercise bike by another inmate, Matthew Charles Johnson.
Williams enlisted the help of others willing to perform the contract killings in exchange for large payments of cash. At the time of his death, he was in the maximum security Acacia unit of HM Prison Barwon near Geelong. Williams would have been 71 before he was eligible for parole.
Williams attended Broadmeadows Technical School, leaving in Year 11. Williams spent much of his childhood in Western Melbourne with his friends and older brother Shane who died of a heroin overdose in 1997. He was married to convicted drug trafficker Roberta Mercieca (born 23 March 1969), with whom he had one daughter, Dhakota, born 10 March 2001. Williams held various labouring jobs before opening a children's clothing store in partnership with his wife, which eventually failed.
On 25 November 1999, Williams, along with his father, George and another associate, was arrested and charged with drug trafficking after a raid on a Fir Close Unit in Broadmeadows illegal drug factory. In excess of 25,000 amphetamine tablets were seized by police, estimated to be worth up to $20 million AUD.
Williams, who described himself as a semi-professional gambler, was banned from the Crown Casino complex on 2 April 2004 by police commissioner Christine Nixon under the Casino Control Act. Williams' mother Barbara was found dead in her Melbourne home on 22 November 2008. She had been suffering from depression.
On 13 October 1999, Williams was shot in the abdomen by Jason Moran because he owed the Morans thousands of dollars. This event gave rise to a lengthy underworld war known popularly as the Melbourne gangland killings. In 2002 after meeting through a mutual friend Tony Mokbel, Carl Williams would court the services of the murderer Andrew Veniamin as his right-hand man until late 2003.
Mark Moran was shot on 15 June 2000 after arriving at his home in Aberfeldie. Williams was due to stand trial for his murder, but the charge was dropped when he pleaded guilty to other murders.
Jason Moran and associate Pasquale Barbaro were fatally shot while sitting in Moran's car at a football club in Essendon, on 21 June 2003. Williams ordered two associates to carry out the murder. The location of the shooting was behind the Cross Keys Hotel in Strathmore, Victoria. The murder was witnessed by six children aged 6 and under. There had been children in the car that the shotgun was fired at.
Mark Mallia was an associate of murdered underworld criminal, Nik Radev. At 8.05 am on 18 August 2003 a fire was reported in a stormwater drain in Sunshine. Fire brigade members attending to the fire recovered a wheelie bin containing the remains of a charred body inside, later identified as Mallia.
Marshall was shot outside his luxury South Yarra home in front of his five-year-old son on 25 October 2003.
Lewis Moran was fatally shot in the inner-city Brunswick Club on 31 March 2004. Williams pleaded guilty to his murder.
On 28 February 2007, Williams pleaded guilty in the Supreme Court of Victoria to the murders of Lewis Moran, his son Jason Moran and Mark Mallia (whose name was initially suppressed by the court).
Williams also pleaded guilty to conspiracy to murder gangland rival Mario Condello. A suppression order prevented the media from reporting this until the day of sentencing. Under a deal with police, Williams was not charged for his alleged involvement in orchestrating the murder of Mark Moran, Jason Moran's half brother.
It was also revealed that Williams was serving a sentence of 21 years for the 2003 murder of Michael Marshall. The outcome of this trial had previously been suppressed.
On 19 April 2010 News Limited newspapers including the Herald Sun revealed that Victoria Police were paying $8000 in school fees for Williams' daughter. The reason for the payment was not revealed at the time. However, during the 2011 murder trial, it was revealed Williams had turned informant and had struck a deal with Assistant Commissioner Simon Overland. Williams gave information on several unsolved murder cases believed to have involved corrupt officers and it was also revealed his murderer may have been implicated in at least one. Williams' lawyer Rob Stary said Williams was upset about the publication of the story.
There was speculation that the police may have agreed to pay the school fees in exchange for information, and that publication of the story may have led to Williams' death. The Herald Sun has defended its publication of the story.
On 19 April 2010, Williams died from head injury while incarcerated at Barwon Prison. He was struck with part of an exercise bike by another inmate, Matthew Charles Johnson, who was convicted for the murder, and sentenced in December 2011 to 32 years in jail.
Williams' funeral was held on 30 April 2010 at St Therese's Catholic Church in Essendon. He was buried in a golden coffin. In January 2011 it was reported that Williams' resting place consisted of a nameless plot, without a headstone.
The circumstances of his death were investigated by the Victorian Ombudsman. A report critical of Corrections Victoria (for approving Williams to share a cell with Johnson) was released in April 2012. Two months later in June 2012, the Department of Justice Secretary Penny Armytage resigned and earlier in May the Corrections Victoria Commissioner Bob Hastings had resigned.