The New South Wales coroner will hold an inquest into the death of murdered environment officer Glen Turner, who was gunned down by a farmer in 2014 in the state's north-west.

The father of two had been investigating illegal land clearing on Ian Turnbull's property, near Croppa Creek.

Turnbull, 79, was found guilty of murdering Mr Turner and sentenced to 35 years' jail but died in custody from a heart attack in March.

A spokesperson for the NSW Coroner's Court has confirmed to Lateline that an inquest into Mr Turner's murder will be held in early 2018.

Mr Turner's wife, Alison McKenzie, had been pushing for an inquest.

She said she wants to know why the NSW Government allowed the illegal land clearing investigation on the Turnbull property to proceed for nearly two-and-a-half years.

"I don't want Glen's death to be in vain and I want people to know the truth," she said.

"The trial of landholder Ian Turnbull was one thing but so many questions came up during it. We need answers to those questions."

The family also wants to know what action the NSW Office of Environment and Heritage took over an earlier death threat by Turnbull against Mr Turner, the details of which emerged during the trial.

Glen Turner's wife Alison McKenzie (l) and sister Fran Pearce (r) had both called for an inquest into his death. ( AAP: Paul Miller )

Ms McKenzie said almost two years before Mr Turner was murdered he was at the Turnbull property to serve a notice regarding some clearing that had been planted over with a crop.

Ian Turnbull died in custody in March. ( AAP: Dan Himbrechts )

"Glen said something like 'we won't be making you pull up the crop' and Turnbull said to him 'not if you value your life you won't'," she said.

"When Glen said 'I'll have to report that as I take it as a threat', he said 'you can take it any way you want. I'm an old man, I can do what I want'."

The call for an inquest into Mr Turner's death had been supported by the NSW and Commonwealth public sector unions.

Earlier, the Office of Environment and Heritage said Mr Turner's death was a tragedy and the safety of staff undertaking investigations was paramount.

Changes to the New South Wales Native Vegetation Act will come into force next month, giving farmers more power to manage their own land.