It was previously rumoured that the actress would appear in the online series, subtitled Web of Lies.
Entertainment Weekly now reports that the former Dollhouse star will voice the lead role in the project, described as an animated "motion comic".
The series is expected to launch prior to the Starz launch of Torchwood: Miracle Day on July 8. Subsequent instalments will then tie in to episodes of the television series.
Web of Lies will consist of ten three-minute videos and will also feature the voice talents of Torchwood stars John Barrowman (Captain Jack Harkness) and Eve Myles (Gwen Cooper).
Former Buffy writer Jane Espenson will co-write the web-series alongside Ryan Scott. Espenson has scripted the third, fifth and seventh episodes of Miracle Day and co-wrote the eighth instalment with Scott. She has also co-written the season finale alongside Torchwood creator Russell T. Davies.
Torchwood: Miracle Day will air on Starz in the US and on BBC One in the UK.
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