David Morris has been found guilty for the second time of beating to death four members of the same family at their Clydach home seven years ago.
The judge at the Newport Crown Court trial sentenced him to life. "Life should mean life and he should never be released," he said.
Morris, 44, from Craig-cefn-parc in the Swansea Valley, had denied the charges.
Fuelled by drink and drugs, the former labourer murdered Mandy Power, 34, her two daughters and their grandmother.
The unanimous verdict brings an end to a tumultuous seven-year investigation - the biggest hunt in Welsh criminal history.
It is the second time Morris - who has a long criminal record and a history of violence - has been found guilty of crimes described in court as "carnage" and "Wales' worst murders".
Judge Mr Justice McKinnon told the jury: "Words cannot convey the severity of the injuries inflicted upon them."
The court heard that the family were subjected to 'grotesque violence'
The retrial began in May after his previous convictions were quashed on appeal. The second trial jurors were told how the family were killed in "a massacre".
Violence exploded at 9 Kelvin Road, Clydach, near Swansea, south Wales, on Saturday, 27 June 1999. Morris sexually assaulted and killed Ms Power before inflicting devastating head injuries on her daughters - Katie, 10, and Emily, eight.
Their 80-year-old disabled grandmother, Doris Dawson, was murdered as she lay in bed.
It is thought one of Ms Power's daughters may have witnessed her mother being attacked and tried to come to her rescue.
The court heard that she may have tried to fight Morris off with a 4ft-long fibreglass pole which the girls often played with around the house.
It was that pole that Morris - a father-of-three and grandfather - used on a "murderous spree".
After washing his clothes in the shower, Morris then lit a series of fires in the semi-detached house in Kelvin Road, Clydach, in an attempt to destroy any evidence.
When firefighters were called to the house later, the bodies of Ms Power, a divorcee, and her children were laid out on the landing.
Earlier that day Morris had been drinking in a nearby pub, the New Inn. His grudge against Ms Power - he disapproved of her friendship with his girlfriend, Mandy Jewell - was evident.
The trial heard that the women had had "a big fall-out" a few weeks previously, and Mr Morris "nursed a particularly strong antipathy towards Mandy Power".
Morris had argued with Ms Jewell in the New Inn and she left the pub. A fellow drinker recalled how Morris appeared to be very angry.
"His eyes were big and wild and manic and he was very quiet. It was frightening and I don't frighten easily," she said.
Morris had also spoken viciously about Ms Power calling her "evil" and growing more angry if anyone jumped to her defence.
The prosecution said that after closing time, an incensed Morris called round to Kelvin Road to confront Ms Power about whether his girlfriend was seeing other men.
He had been drinking and had taken amphetamines. Inside Kelvin Road, something happened to trigger "an explosion of violence".
Firefighters were called to the house and discovered four bodies
As he attacked Ms Power, a gold necklace was torn from his neck. It was recovered, bloodstained, from the house at one of the points of most extreme violence.
Morris denied that the chain was his right up until days before his original trial in 2002.
Then he admitted it did belong to him but said it was broken and that he had left it in Ms Power's kitchen when he called round there for a coffee the day before her death.
He claimed to have had sex with Ms Power that day and did not want his girlfriend to find out.
Morris went to some lengths to try to fool the police. He got hold of a new, identical chain and rubbed it in cement and damaged the clasp to make it look more like his old one.
Morris was not charged with the murders for some time. Initially, suspicion fell on the married woman with whom Ms Power had been having a secret lesbian love affair.
Former South Wales Police officer Alison Lewis was married to another officer Stephen Lewis.
Along with Mr Lewis's brother - also a policeman - they were arrested in connection with the murders but never charged.
On hearing the news about the murders, Ms Lewis tried to throw herself out of her bedroom window and was admitted to a psychiatric hospital suffering from "extreme grief reaction".
She said they had an "intense relationship" since meeting her while she was playing women's rugby for a team in Swansea and Ms Power was among the spectators.
Now divorced, she told the court that she would have given her own life to protect Ms Power and her daughters.
Giving evidence during the trial she broke down in the witness box and said the only things she was guilty of was being in bed next to her husband as Ms Power fought for her life and those of her family.
Following the verdict, Mandy Power's family welcomed the verdict, but Morris' sister, Debbie, said his family would "fight this every step of the way".