Daniel Eckersley was in a drug-induced psychosis and convinced his partner was poisoning his children when he stabbed her to death in front of them.
Ecklersley will spend at least 14 years behind bars for attacking 36-year-old Amanda Harris with a kitchen knife, while their son tried to intervene at Cranbourne North in Melbourne's southeast on July 7, 2018.
Ms Harris' distraught mother sobbed and screamed as the 40-year-old killer was jailed in the Supreme Court of Victoria on Thursday for a maximum of 18 years.
"You bastard," the victim's mother yelled.
"What about his kids? This is bull****."
The woman continued to sob and yell at the murderer as he was led out of the courtroom.
Eckersley was in a psychotic state caused by prescription drug abuse when he took a hammer to the kitchen and then stabbed Ms Harris in the head, neck, chest and upper body.
Their son tried to intervene, but Eckersley kicked him away and then set the couch on fire using a cigarette lighter.
He had been taking far more than the recommended amount of the opioid drug Tramadol and anti-depressant Pristiq when he became deluded and convinced Ms Harris was poisoning him and their three children.
Justice John Champion described the killing as an act of "savagery" committed against a defenceless woman.
"The impact on your children of seeing you murder their mother is difficult to fully imagine," the judge said.
"Having committed this awful crime, you did not then help ... but acted to destroy her body and the scene by attempting to burn down your home with her body in it.
"You treated your children callously after they had witnessed your brutality by driving them away and telling them to tell others Ms Harris had committed suicide."
But Justice Champion handed Eckersley a lesser sentence because he was suffering from psychosis.
"It must be clearly acknowledged that when you committed this horrible and intensely violent crime, you were in a severe acute psychotic state," he said.
Eckersley had a history of abusing prescription and illicit drugs as well as alcohol.
His mental state deteriorated markedly in the lead-up to the murder.
Days before she was killed, Ms Harris took a "depressed, sad and tearful" Eckersley to the doctor and was so concerned she also contacted his family.
"(Ms Harris) was a loving and caring partner and mother," Justice Champion said.
"You have deprived your children of both their mother and also of you. Your actions have destroyed your own family."
Eckersley recovered quickly from his psychotic episode after being arrested.
The judge accepted the killer was truly remorseful and did not believe he posed a continued threat to the community, with the caveat that he never again used the drug Tramadol.
Psychotic reactions are a rare side effect of the commonly-used medication, but Justice Champion will ask Victoria's coroner to look at whether doctors should be given more information about the risks involved.
Eckersley has spent 572 days in pre-sentence detention and must serve 14 years before being eligible for release on parole.
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Australian Associated Press