Nikki Roper killed 21-year-old mother-of-one Alexsis Tovizi with a sleeper hold at her Christchurch flat in 2010 - just five days after being released from prison where he was serving a sentence for choking her.
As he left jail in 2010, the unemployed 24-year-old he told an inmate: "I'm going to kill the b****''.
Roper, who has 'Alexsis' tattooed under his left eye, had denied strangling the student social worker on the night of December 4, 2010 at her Stanmore Rd flat.
He claimed she died of natural causes related to binge drinking.
But after a seven-day trial, the jury took just four hours to convict him.
When Alexsis' mother Cheryl Tovizi gasped "Thank God'' at the verdict, Roper shouted "F*** up b****'' and then leapt out of the dock and lunged at someone in the public gallery who'd given evidence against him.
He was pounced on by four court security staff and dragged into the cells.
When he was brought back into the room at the High Court in Christchurch, Roper turned to the gallery again and said: "Just remember what happens when you nark on the Mongrel Mob, eh.''
During the trial, the Crown told how Roper was "obsessed'' with his on-again-off-again girlfriend.
Her mother, Cheryl, had taken out a protection order out against him but said her daughter was often in touch with him.
When Roper was released from a prison on December 1, 2010, he allegedly told an inmate he was going to kill his girlfriend because she had cheated on him.
"Five days later, she was dead,'' said Crown prosecutor Pip Currie, adding it was a killing fuelled by jealousy and revenge.
After the trial, Mrs Tovizi called for an urgent law change to protect victims of psychological abuse, particularly where non-contact conditions are in place, and to update legislation to include modern communications.
"Abusers now have more ways of contacting victims than ever before,'' she said.
"Our laws need to change to protect victims from the calculated way abusers use technology to continue to violate non-contact protection orders.''
