The 50-year-old mother blinked but appeared emotionless as four guilty verdicts were read out by the jury's foreperson to a full court-room of onlookers on Monday afternoon.
Patterson, who took the stand for eight days during her trial, claimed she had not intentionally poisoned her lunch guests with beef Wellington parcels.
She claimed deaths of three members of her estranged husband Simon's family were a terrible accident, and she may have accidentally included foraged mushrooms in the meal.
Don and Gail Patterson, 70, and Gail's sister Heather Wilkinson, 66, all died in hospital days after eating the meal, while Ian Wilkinson became sick but survived.
Heather Wilkinson and Don and Gail Patterson died in hospital after eating Erin Patterson's meal.
Prosecutors laid out an extensive circumstantial case during the trial in Morwell, regional Victoria, to prove the poisoning event was deliberate.
This included evidence from sole lunch survivor Ian Wilkinson, who said Patterson had served individual beef Wellingtons to her guests on different plates to her own.
The prosecution accused Patterson of telling a series of lies to police, including that she did not forage for mushrooms in the meal and did not own a dehydrator.
She lied about it to public health investigators, who were searching to find the source of poisonous mushrooms after Patterson claimed they may be from an Asian store.
Patterson lied to doctors, nurses and toxicologists while they were trying to identify why her lunch guests were sick and save their lives at hospital.
She revealed for the first time that she enjoyed foraging for wild mushrooms when she was in the witness box, admitting she started mushrooming in 2020 during the pandemic.
"They tasted good and I didn't get sick," she told the jury about preparing and eating wild fungi for the first time.
After hearing more than two months of evidence, a jury of 14 was whittled down to 12 jurors who retired to deliberate on their verdicts one week ago, on June 30.
They returned after deliberating for seven days with a four guilty verdicts, convicting the 50-year-old woman of three murders and one attempted murder.
Patterson now faces a sentence of up to life in prison.
She will return to the court for a pre-sentence hearing later this year.
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