Deadline reported Tuesday that Lynskey, 44, will play Betty Gore in the new limited series.
Variety confirmed Lynskey's casting.
Lynskey joins previously announced star Jessica Biel, who will portray convicted killer Candy Montgomery.
Candy centers on the real-life story of Montgomery (Biel), a Texas woman who killed Gore (Lynskey) in 1980. The series explores why Montgomery, a wife and mother living in the suburbs of Dallas, killed Gore, her friend from church, with an ax.
Lynskey's Gore is described as a teacher, wife and mother who just wanted to be a part of her small Texas community.
Robin Veith wrote the pilot script and will executive produce with Biel, Nick Antosca, Alex Hedlund, Michelle Purple and Michael Uppendahl. Uppendahl will also direct the pilot.
Lynskey is known for playing Rose on Two and a Half Men and Molly Strand on Castle Rock. She will also star with Christina Ricci and Juliette Lewis on the Showtime series Yellowjackets.
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