Erin Patterson will spend the rest of her life in prison after an Australian appeals court rejected her challenge and increased her non-parole period.

The 51-year-old was originally sentenced to life imprisonment with a 33-year non-parole period for killing three relatives by serving beef Wellingtons laced with death-cap mushrooms.

On Friday, the Victoria Court of Appeal ordered that Patterson never be released, agreeing with prosecutors that the original parole term was inadequate.

All three judges also dismissed her attempt to overturn the convictions stemming from a family meal she hosted at her rural Leongatha home in July 2023.

Patterson claimed the death-cap mushrooms were added accidentally. Her mother-in-law Gail Patterson, father-in-law Donald Patterson and Gail's sister Heather Wilkinson died in hospital within six days of the July 2023 lunch.

She was also found guilty of attempting to murder Heather's husband, Ian Wilkinson, a local pastor who survived the poisoning.

Last year, Patterson received three life sentences for murder and a 25-year term for attempted murder, with parole eligibility after 33 years.

She appealed the verdict while the Director of Public Prosecutions appealed the sentence, arguing the non-parole period was "manifestly inadequate".

During the appeal, counsel Richard Edney highlighted a "catastrophic" error that placed jurors in the same hotel as a police witness, journalists and prosecutors, arguing it undermined the verdicts.

Justice Stephen McLeish rejected those arguments, denied the appeal and sided with the DPP, meaning Patterson will remain incarcerated, according to 7News.

McLeish described the crimes as "extraordinarily cold and calculated" and a "cruel breach of trust".

Patterson can still seek review by Australia's High Court.

The court noted that, despite Edney's concerns, there was no evidence jurors contacted anyone at trial, though the defence pointed out the crossover occurred during jury deliberation week.

Another disputed issue involved the prosecution's use of Patterson's activity on the foraging site iNaturalist and mobile-phone tower data, which placed her near two reported death-cap sightings.

Prosecutors said her phone connected to towers near both sites, and hours after visiting one location she purchased a food dehydrator to process the mushrooms for the fatal Wellingtons.

CCTV footage showed Patterson disposing of the dehydrator at a local dump; later analysis found traces of the deadly mushrooms.

'MUSHROOM' MURDER TIMELINE

All the twists & turns that led to Erin Patterson being jailed for life

2021-22 - A 48-year-old man, believed to be Patterson's ex-husband Simon, falls ill after three separate meals.

July 29, 2023 - The lethal mushroom lunch occurs.

July 30 - Gail and Donald Patterson and Heather and Ian Wilkinson are rushed to hospital; all die except Ian.

August 5-7 - Police search Patterson's home, question her and name her an official suspect.

November 2 - Patterson is arrested and charged with three counts of murder and five counts of attempted murder.

May 7, 2024 - She pleads not guilty to the eight charges.

April 29, 2025 - Trial begins; prosecution drops three attempted-murder charges related to ex-husband Simon.

July 7, 2025 - Jury finds Patterson guilty.

September 8, 2025 - She receives life imprisonment with a 33-year non-parole period.

When sentencing, the judge said the source of the mushrooms was irrelevant because it was clear Patterson had used them.

Patterson continues to maintain she unknowingly used foraged death-cap mushrooms.

Prosecutors lodged 35 complaints during the proceedings, prompting claims of unfairness.

Police also allege Patterson may have tried to poison her ex-husband Simon Patterson on three occasions between 2021 and 2022.