Just hours after the brutal murder, he drove to Cheshunt railway station in Hertfordshire, where he threw himself in front of an express train.
He suffered horrific injuries, including a severed right arm and left hand, but survived.
When police went to his home in Islington, north London, they discovered Best's body in the living room with a belt wrapped around her neck, and a blood-stained claw hammer nearby.
The wheelchair-bound defendant had initially admitted her manslaughter on the grounds of diminished responsibility, but denied her murder.
However, as prosecutor Mark Heywood QC prepared to open the case to the jury at Old Bailey on Tuesday he changed his plea and admitted murder. He will be sentenced on Friday.
Heywood said: "This is a man who is controlling and violent to the women in his life and who, when crossed, will kill."
Garage worker Johnson was born in Jamaica and moved to the UK in 1980.
The following year he was convicted by a jury at Stafford Crown Court of killing his wife, Yvonne Johnson.
He hit the mother-of-two with a vase after an argument before pushing her over the balcony of their ninth-floor flat in Wolverhampton.
He was convicted of manslaughter on the basis of provocation and served less than five years.
In March 1993, he was again convicted of manslaughter after killing his then partner, Yvonne Bennett.
The couple, who had a daughter, had moved from Wolverhampton to Finsbury Park in North London, where Johnson strangled Bennett with a belt after discovering she had an affair with another man.
Johnson then tried to hang himself from a tree but failed after the string he used snapped.
Doctors concluded he was depressed and had a personality disorder.
He was found guilty of manslaughter having claimed diminished responsibility and was sent to a psychiatric unit, where he served just two years.
After his release in 1995 he met Best. She had moved to Tottenham in north London from Manchester with her children.
Judge Richard Marks QC remanded him into custody to be sentenced on Friday.
Detective Sergeant Danny Yeoman, of Scotland Yard, said: "This was a vicious attack and I hope the conviction gives Angela's family some measure of comfort and closure."