A farmer who shot and killed a New South Wales environmental officer over a land dispute has been jailed for a minimum of 24 years.

Key points: Turnbull sentenced to 35 years in prison with a non-parole period of 24 years

Turnbull sentenced to 35 years in prison with a non-parole period of 24 years Judge said it was almost certainly a de facto life sentence

Judge said it was almost certainly a de facto life sentence Glen Turner's family expressed relief at "a good result"

Ian Turnbull was found guilty last month of the 2014 murder of Glen Turner, near Moree, in north-western New South Wales.

Turnbull was sentenced to 35 years in prison with a non-parole period of 24 years.

In sentencing, Justice Peter Johnson told the Supreme Court in Sydney that the 81-year-old intended to kill Mr Turner.

The judge said it was a de facto life sentence due to Turnbull's age.

"I have taken into account that this sentence will almost certainly constitute a de facto life sentence with the offender dying in custody before the expiration of the non-parole period," the judge said.

"I am satisfied that no lesser sentence is appropriate in all the circumstances of the case."

Justice Johnson told the court he was not persuaded that Turnbull was suffering from major depression at the time of the murder.

"I am satisfied that the offender suffered at the time of the offences an adjustment disorder which arose from the combination of stressors which operated upon him," he said.

NSW environment officer Glen Turner was fatally shot north of Moree in 2014. ( Supplied by the Turner family )

"He had developed entrenched thought processes concerning the OEH [Office of Environment and Heritage] and in particular Mr Turner."

During the trial the court heard Turnbull was facing prosecutions by OEH in the Land and Environment Court over illegal land clearing, which he continued to do after officially being told to stop.

He believed he was being singled out by authorities but admitted he had not had a conversation with Mr Turner for more than two years before shooting him dead.

Turnbull's son Grant also testified that the family would have faced financial ruin if they had lost their legal battle with the OEH.

Turnbull intended to kill environmental officer, court heard

During the trial the court heard Turnbull drove out in search of Mr Turner, after learning he was in the Croppa Creek area near Moree in July 2014.

Turnbull admitted taking his rifle and firing several shots at Mr Turner.

He had told the jury earlier in the trial that calmness came over him after he fired the first of three shots to hit Mr Turner, over a period of at least 20 minutes, at the side of a road.

It happened in front of fellow environment officer Robert Strange, who pleaded with the 81-year old to let them go, so he could get help for his seriously wounded colleague.

Turnbull refused, telling Mr Strange the only way Mr Turner was leaving was in a body bag.

After firing his final and fatal shot, Turnbull said he was going home and the police would know where to find him.

Verdict a relief: Turner family

Mr Turner's partner and sister described their horror at the circumstances of Mr Turner's death during the trial.

Sorry, this video has expired Glen Turner's partner Alison McKenzie (left), and sister Fran Pearce, speak outside court

His partner Alison McKenzie said he was treated like a "feral pig" and she could not comprehend how someone could do that to another person.

Ms McKenzie said today the verdict was a good result.

"It's the end of a long road for us but it will never bring Glen back, so no matter what sentence he was given, it's never going to change what happened and [we're] just glad that justice has prevailed," she said.

Mr Turner's sister Fran Pearce said the verdict was a relief.

"It's a hard emotion to describe, so pleased doesn't really cover it. It's very relieving. It's probably more than we even hoped for," she said

"We hoped that he'd die in jail, to be honest, because Glen didn't get a chance to go home to his family, so we think that's fair."

Ms Pearce said the family was grateful the judge acknowledged Mr Strange, who "did his best to help" Mr Turner.

"He's really the forgotten victim in this and he often gets overlooked. He's going to suffer the rest of his life for what he saw and what he tried to do, so we're really grateful that he was acknowledged in the sentencing," she said.

"I think the other two people that need to be remembered are Jack and Alexandra. They don't have their father for the rest of their life, so he needed to be sentenced to a long time for that."

'This will happen again' if vegetation laws not changed: son

Turnbull's son Grant Turnbull said a similar tragedy would happen unless the state's native vegetation laws were changed.

Turnbull's wife, Robeena Turnbull, leaving Sydney's Supreme Court after the verdict. ( AAP: Paul Miller )

Mr Turnbull said the Vegetation Act was unworkable.

"But the frustration that's out there, it's not just my father, it's many people out in rural New South Wales that are extremely frustrated, extremely frustrated with the way it's administered and the act itself, it just needs to change," he said.

"If the native vegetation acts aren't changed in this state, unfortunately this will happen again.

"It just shouldn't happen to two more families. The politicians need to listen. They need to listen to the people.

"The way it's administered. The way this act is administered, that's what needs to change.

"It doesn't need to be scrapped, it just needs to be made workable.

"I have never been to any meeting where anyone has said lets go back to the old way of doing things, it is simply 'lets get something that is workable for the people of New South Wales'."