Ian Thomas, 38, was found guilty by a Supreme Court jury of strangling his mother Pauline, 63, and shooting then bludgeoning his father Bill, 65, at the family farm on April 21, 2013.

Thomas, who had previously been living in Western Australia, had been staying with his parents when he used cable ties to strangle his mother, before shooting his father and then repeatedly hitting him in the head with a pick-axe.

He claimed during his trial it was his father who had murdered Mrs Thomas, and that he had shot his father in self-defence, but the jury rejected this testimony.

At a plea hearing, Theo Kassimatis, for Thomas, said it is open to Justice Lex Lasry to impose a life sentence but he urged him not to. He said given Thomas' release date was so far away, it was not possible for the court now to find whether he would still pose a threat in the future.

Mr Kassimatis said the crimes were provoked by the "truly awful treatment" the former electrician had endured "at the hand of his father" during his childhood and adolescence, while his mother "stood by and watched".

"He maintains his childhood and early adolescence was stained by regular verbal and physical abuse," he said.

"It is a form of provocation, especially when it occurs in early childhood".

Prosecutor Peter Rose said two of Thomas' siblings refuted claims the five Thomas children had been raised in an abusive environment.

"[Sisters] Donna and Jacinta describe a very different type of upbringing," Mr Rose said.

He said Thomas' actions show "a fair degree" of pre-planning.

"We really have a situation where he has thought about – although he accepted his parents hospitality – exacting vengeance," Mr Rose said.