Cory Jefferies has been found guilty of murdering his long-time partner Kim Richmond.
Jefferies, 46, has been on trial in the High Court in Hamilton, for the murder of 42-year-old Richmond in 2016.
Her body was discovered in Lake Arapuni in June 2017, 10 months after she disappeared.
Jefferies admitted manslaughter but denied her murder.
After six hours' deliberation last Friday, the jury retired for the weekend.
It took just half an hour this morning for the jury to return a verdict of guilty of murder.
Jefferies stood quietly as the the decision was read out.
Members of Ms Richmond's family quietly showed their satisfaction at the verdict, having been warned earlier by Justice Fitzgerald not to make any comment in court.
No members of Jefferies family or friends were in court for the verdict.
Friends and family of Ms Richmond were wearing red roses as a sign of support for her as it was her favourite flower.
The family left the court refusing to make any statement or comment to waiting media.
Jefferies was given a first-strike warning and will be sentenced on 7 September.
The Crown said Jefferies killed Ms Richmond in a seven-minute period on a drive home from a late night at a function near their farm at Arohena in South Waikato.
Prosecutor Ross Douch last week told the court her fitbit device showed Ms Richmond had a settled heart beat as she and the accused started to drive home.
He said it stopped recording a heart beat at about 3.43am, around the time their vehicle was stopped on the highway before it continued on.
Mr Douch said while it has never been found, the fitbit automatically downloaded information to the cloud where it was later recovered.
He said there could be a number of explanations why Ms Richmond's heart beat stopped being recorded on the device.
"One is the fitbit device was no longer attached to her, another was it developed a fault, the third of course is that her heart had simply stopped beating."
Both Jefferies and Ms Richmond's cellphones showed the vehicle had stopped on the road for a few minutes before moving again.
Ms Richmond's cellphone shows the vehicle went to the area of the boat ramp at Lake Arapuni and there is a period of pause, the cellphone didn't travel on.
Jefferies' cellphone showed it then tracked back to the farm.
"But at a speed that indicated quite clearly he wasn't in a motor vehicle but was on foot," Mr Douch said.
Kim Richmond Photo: Supplied
The Crown said Ms Richmond had developed a romantic relationship with a neighbour, Alfons Te Brake.
Mr Te Brake told the jury Jefferies had discussed it with him on a few occasions, and that the accused had told him he wanted her gone and had threatened to kill her.
Under cross examination by the defence, Mr Te Brake said he wasn't 100 percent sure Mr Jefferies had used the words, kill her.
Jefferies' lawyer, Thomas Sutcliffe, told the court that the couple's 26-year relationship had been going through difficult times, but they had spent an uneventful night together at the social function.
He said something happened between them on the seven-minute drive home.
"The available evidence will show you that whatever it was, it appears to have been relatively brief, matter of minutes, but whatever it was it resulted in the death of Kim Richmond."
He went on to say, "Mr Jefferies is therefore guilty of culpable homicide, in that he committed the offence of manslaughter, not murder."
A police interview conducted just over two weeks after Ms Richmond was reported missing was also shown in court.
In it, Jefferies is seen telling police he had never threatened or beaten her because he was not that sort of person.
When told that other people reported he had threatened her, Jefferies said that it was not true.
He told police she drove off in their ute shortly after they arrived home from a social function.
And said he saw her turn at the end of the drive and that was the last he ever saw of her.
He said he started texting her from the next morning, but got no reply.
Meanwhile, Forensic pathologist who examined Ms Richmond, Rexson Tse, earlier told the court he was unable to determine the cause of death due to the decomposition of her body.
He said there was no detectable sign of violence, fractures, or any blunt force injury.
And he could not rule out suffocation or strangulation.
A police officer who oversaw the recovery of Ms Richmond's body once it was lifted from the lake said her chest and stomach were free from any clothing.
There was an empty plastic shopping bag near her head and torso, he said.