Patterson, 52, appeared on a video link from prison as three Victorian Court of Appeal judges handed down their decision on Friday morning.
She had been seeking to overturn her murder and attempted murder convictions, arguing she suffered a substantial miscarriage of justice during her high-profile trial.
But the court dismissed her appeal and instead granted the prosecution's appeal against her sentence.
Justices Stephen McLeish, Lesley Taylor and Peter Kidd agreed her life sentence with a non-parole period of 33 years was manifestly inadequate.
They set aside that jail term and instead re-sentenced Patterson to life behind bars without parole.
"This offending was extraordinarily cold and calculated," the judges said.
Patterson's failed appeal bid means her convictions over the death cap mushroom-laced lunch still stand.
She faced a months-long trial in 2025 accused of deliberately serving the deadly beef Wellingtons to her former in-laws Don and Gail Patterson, 70, and Gail's sister Heather Wilkinson, 66.
The three guests died after the July 2023 lunch at Patterson's Leongatha home, in regional Victoria, while Heather's husband Ian fell seriously ill from the meal but survived.
The jury heard from more than 50 prosecution witnesses throughout the trial before Patterson entered the witness box for eight days.
The prosecution and defence then spent a week delivering their closing arguments before Justice Christopher Beale provided his directions to the jury.
After six days of deliberations, the jury returned four 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 during her high-profile trial and her convictions should be quashed.
Barrister Richard Edney pointed to the "catastrophic" decision to sequester jurors in the same hotel as the lead detective and prosecution team during their verdict deliberations.
Patterson had also been "forced" to give evidence during her trial to show she always had an interest in foraging for mushrooms, the defence said.
The cross-examination from the prosecutor had been unfair and oppressive, and the prosecution closing address was also "problematic", Mr Edney argued.
Victoria's top prosecutor Brendan Kissane KC had defended the convictions, while arguing the only substantial mistake was her life sentence including a non-parole period.
Justice Beale jailed Patterson for life but gave her a chance at parole after 33 years served.
She has served just shy of three years in custody, having been arrested by homicide detectives at her home on November 2, 2023.
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