The Crown case against Ian Thomas, 38, was that he strangled his mother after an argument, before laying in wait for his father, shooting him in the chest and caving his head in with a wooden pickaxe handle.

The key witness, Mr Thomas' married lover Jacinta Emselle, told the Supreme Court jury he had confessed when they met at the Cremorne Hotel in Geelong the day after the alleged murders.

She said Mr Thomas was drinking a beer and reading the paper when he told her, with a strange smirk on his face, "Let's just say my parents are no longer with us".

Mr Thomas denied ever confessing to the crime, claiming he had been out drinking alone in bushland near the farm when he came home to find his mother lying dead in the shed covered by a drop sheet and his father waiting for him in the master bedroom armed with a single-barrel shotgun.

Mr Thomas said he managed to wrestle the shotgun away from his father before shooting him in self defence.

He claimed he then repeatedly hit his dead father's head with the axe handle because of what he had done to his mother.

The jury on Thursday found Mr Thomas guilty of murdering his parents, William, 65, and Pauline, 63, at their Great Alpine Road home between Wangaratta and Tarrawingee, on April 21, 2013.

Thomas, who showed no emotion when the verdicts were read out, was remanded for a pre-sentence hearing on a date to be fixed.

Mr and Mrs Thomas had been married for 40 years and had five children.

Three of the children — Bernadette, Ian and John — claimed their father regularly beat them when they were growing up with a belt he'd nicknamed "Joey".

The other two children — Jacinta and Madonna — denied ever being physically abused by their father.

In his closing address to the jury, Crown prosecutor Peter Rose, QC, said there was nothing to suggest any animosity between William and Pauline Thomas on the day they died.

"They were a loving couple. There's no suggestion they weren't getting on that day," Mr Rose said.

The prosecutor reminded the jury of Ms Emselle's evidence where she talked of Mr Thomas' confession.

"She [Ms Emselle] gives evidence of walking into the hotel and Ian sitting there having the beer, says he has ordered some food," Mr Rose said.

"Strange look on his face. And that's effectively when he tells her that he's killed his parents. Tells her, 'Mum was annoying me, nagging me, driving me crazy ... come out of the shed, we had an argument, put my hands around her neck and squeezed until she fell to the floor'."

Mr Thomas later changed his clothes and "prepared himself for his father's return in order to murder him also," the prosecutor said.

Defence barrister Theo Kassimatis told the jury Ms Emselle, who met Mr Thomas at a Queensland rehabilitation clinic for alcohol dependency in 2010, was an unreliable witness given her heavy drinking at the time.

"She's no ordinary liar," Mr Kassimatis said.

"We are talking about gold medal-winning, world champion liar.

"You might think you can't believe a word she said. You might think if she told you it was Tuesday the first thing you'd do is run to a calendar."

On the issue of Mr Thomas' evidence, Mr Kassimatis said the electrician told how his father lay in wait for him, how he had disarmed him and how he shot him in self-defence.

"This wasn't just anyone pointing the shotgun at Ian Thomas, it wasn't just a stranger that he'd come home to," Mr Kassimatis said.

"It was his father. It was the man who had monstered him throughout his childhood ...

"Add to that your father's just strangled and killed your mother, and it might go some way, it might go all the way, to explaining what Ian did to his father after he killed him."

Mr Kassimatis said William Thomas, the man who beat his children savagely when they were young, was the same violent, angry man who killed his wife.

The defence barrister highlighted how the autopsy results showed Pauline appeared to have been hit in the face and William Thomas had bruising on his knuckles, which Ian didn't.

The Crown said the bruising was caused by William Thomas' years of working on the farm.

Mr Kassimatis said William's DNA was also found on Pauline's clothing under her armpits.

"Could he have strangled her in the shed and then lifted her up and dragged her to a spot a little less conspicuous before putting the drop sheet over her?"

Strands of William Thomas' hair were also found on his fingernails and palm of his hand.

The defence barrister asked was William Thomas holding his head after killing his wife and saying, 'F--k, f--k, f--k what have I done? F--k'?

"The evidence is compelling. Bill Thomas killed his wife."

The jury did not agree.