Titled Mushroom Murders: There's More to Unearth, the six episodes will depict the 97 days between the infamous lunch in July 2023 and Patterson's subsequent arrest.
Lynskey revealed the news on stage at the Paramount+ and Ten upfronts, where a slate of new and returning shows was announced, prompting audible gasps from the audience.
The actor said she was "very excited" to take on the role in the new drama series.
"It offers a compelling and unique perspective on the events that made headlines around the world - it's really good," she said.
"Because behind those headlines, there is still so much to unearth."
Patterson was convicted of murder after serving a beef Wellington lunch laced with toxic death cap mushrooms to her estranged in-laws and their relatives at her home in Leongatha, Victoria.
The meal killed her husband's parents, Don and Gail Patterson, and his aunt Heather Wilkinson.
Heather's husband, Ian Wilkinson, also became seriously ill but survived after weeks in hospital.
The case attracted international attention, spawning podcasts, books and television adaptations as audiences became fascinated by the investigation and trial.
In September 2025, Patterson was sentenced to life imprisonment for the murders and the attempted murder, with a non-parole period of 33 years.
"This is an ambitious series that brings a gripping real-life story, that captivated Australia and the world, to the screen with the scale, quality and creative vision audiences expect from Paramount+," Beverley McGarvey, President Network Ten and Head of Streaming, Paramount Australia, said.
"We are also thrilled to welcome Melanie Lynskey, whose remarkable talent will be integral to the series both on screen and as an executive producer."
Lynskey, a New Zealand actor nominated for an Emmy for her role in Yellowjackets, will also serve as an executive producer on the series.
The show announcement comes two days before a court rules whether Patterson should face a retrial.
Patterson is appealing her conviction and her sentence in the Victorian Court of Appeal, arguing she suffered a substantial miscarriage of justice.
Prosecutors are also appealing against her sentence, arguing she should have been jailed for life without the possibility of parole.
The appeal judges will hand down their decision on Friday.
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