Clayton Weatherston has been found guilty of the murder of his former girlfriend Sophie Elliott, whom he stabbed or mutilated more than 200 times at her family's home.
Weatherston, 33, had denied murdering Miss Elliott in Dunedin in January 2008.
The former University of Otago tutor had earlier admitted a charge of manslaughter at the High Court in Christchurch.
Weatherston told the court he was provoked into stabbing or cutting Miss Elliott 216 times due to their volatile relationship, and an attack he claimed she made on him with scissors just before he killed her.
The defence argued Weatherston had a narcissistic personality disorder and lost control when he was provoked by Miss Elliott, 22, who met him when she was a student at the university.
But the Crown argued that Weatherston was not provoked, and the fact he went to her family's home with a knife indicated that he planned to kill her.
The jury of seven men and four women began their deliberations on Tuesday afternoon and continued on Wednesday morning after a five-week trial. They took four-and-a-half hours to reach their verdict.
Weatherston showed no emotion as the verdict was read out. Justice Potter remanded him in custody for sentencing on 15 September.
Elliott family relieved at verdict
Outside court, Miss Elliott's mother Lesley Elliott, who witnessed part of the attack, said the verdict was a relief.
"It was the right decision. It's been a long 18 months for all of us and we needed to see justice for Sophie for her loss of life and also for a lot of other girls that may be in this position.
"We're pleased with the outcome - it's been a hard time and we'd like to thank New Zealand for ... the amazing support," she said.
Mrs Elliott heard her daughter being attacked and desperately tried to get into the locked bedroom. She managed to pick the lock and saw Weatherston on top of her now dead daughter still stabbing her.
Weatherston had claimed he was provoked, but Mrs Elliott said that was never the case and is angry that the defence of provocation was able to go so far.
However, she is relieved the jury believed her version of events.
"Despite what was said there were three of us there ... Sophie, who's not alive, Clayton and myself. And I know what went on in that room - I've absolutely no doubts at all. There was no provocation at that time - it was awful."
Weatherston was 10 years older than Miss Elliott and had had numerous relationships. During the trial, the jury was told he was jealous, possessive and insecure.
Mrs Elliott had disapproved of the relationship and outside court made a plea for girls to listen to their parents.
"I would like girls to value their families, to listen to their mums and dads and friends."
Family hopes Weatherston will get help
Weatherston's family said they hoped their son and brother would now receive the help he clearly needs.
Outside court Weatherston's father, Roger Weatherston, said his family was shocked by what he had done.
"We have been very grateful for the opportunity to listen to the evidence at the trial and now have some understanding of this terrible event that came about.
"We're very sad that we did not recognise that Clayton needed the help that he clearly does and hope that now at least he will receive it."
Mr Weatherston says his family's thoughts are with the Elliott family.
David Chaplow, a forensic psychiatrist who appeared as a witness for the defence, says he saw no signs of remorse from Weatherston.
The two psychiatrists called by the defence told the court Weatherston suffered from a type of personality disorder, manifesting in narcissistic and grandiose behaviour.
Dr Chaplow told Checkpoint on Wednesday that Weatherston is not mentally ill, but will need some professional help before he can function better in society.
He said the chances of Weatherston improving his mental health will depend on his desire to seek treatment.