Williams will play Cammie MacLoud, a mischievous Sottish hacker and the youngest recruit to the gen:LOCK program.
She joins a voice cast that includes Michael B Jordan, who plays the lead character, and David Tennant and Dakota Fanning.
Gray G Haddock has created "gen:LOCK" and is the showrunner.
"Maisie truly sounds exactly like how Cammie does in my head, she is brilliant," he said.
According to Variety, the announcement of Williams' casting was made at RTX London, the UK edition of Rooster Teeth's expo.
Jordan's Outlier Productions is co-producing with Rooster Teeth.
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