Dressed in a royal blue jumper with a ponytail and glasses, Patterson did not visibly react as she learnt her fate in the Victorian Court of Appeal on Friday.
The 52-year-old watched the decision on a video link from the Dame Phyllis Frost Centre where she will spend the rest of her life.
She had been trying to overturn her murder and attempted murder convictions, arguing she suffered a substantial miscarriage of justice during her high-profile trial.
Patterson's lawyers pointed to the "catastrophic" decision to sequester jurors in the same hotel as the lead detective and the "unfair and oppressive" cross-examination the killer faced.
But the court dismissed her appeal, finding the grounds were not made out and she did not suffer a miscarriage of justice.
They instead granted the prosecution's appeal against her minimum 33-year sentence, saying it was inappropriate to set any parole period.
Patterson's sentence of life without parole makes her only the second woman in Australia to be sentenced to such a fate.
The first was NSW woman Katherine Knight, jailed in 2001 after stabbing her de facto husband to death, skinning him and then trying to serve his cooked flesh to his children.
Patterson's decision to serve deadly beef Wellingtons to her in-laws represented a "cruel breach of trust", Justices Stephen McLeish, Lesley Taylor and Peter Kidd said as they re-sentenced her.
"This offending was extraordinarily cold and calculated and stands to be denounced in the strongest terms," the judges said.
"This is a case of such shocking criminality that it is inappropriate to fix a non-parole period."
Patterson deliberately served the death cap mushroom-laced lunch to her former in-laws Don and Gail Patterson, 70, and Gail's sister Heather Wilkinson, 66, in July 2023.
The three guests died after the meal at Patterson's Leongatha home, in regional Victoria, while Heather's husband Ian fell seriously ill but survived.
Patterson's intent to murder was sustained for nearly three weeks, from the time she invited her guests to lunch through to her lies after the meal as her victims suffered, the appeal justices found.
"(Patterson's) conduct was characterised by an elaborate series of deceptions," the judges said.
"The offending was carefully planned and deliberate.
"It represented a cruel breach of trust to members of (her) extended family."
Patterson stared straight ahead and at times closed her eyes as the decision was read aloud.
Her surviving victim Ian Wilkinson was not in court for the decision but his nephew Nathan Patterson and the case's lead detective Stephen Eppingstall were.
Members of the public also filled the public gallery for Friday's hearing, while the decision was livestreamed.
The case has attracted international attention, with reporters from around the globe flocking to the regional town of Morwell for the trial in 2025.
Over the course of 10 weeks, the jury heard from more than 50 prosecution witnesses before Patterson herself testified for eight days.
The jury deliberated for six days before they returned guilty verdicts to the three counts of murder and one count of attempted murder.
At her appeal hearing in August, Patterson's lawyers argued she suffered a substantial miscarriage of justice and her convictions should be quashed.
Victoria's top prosecutor Brendan Kissane KC defended the convictions but argued the only substantial mistake was her life sentence including a non-parole period.
Patterson has 28 days to consider whether she will take her appeal fight to the High Court of Australia.
If she chooses to appeal once again, she will have to file an application for special leave with the court, which would have to accept the application.
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