The Cabin in the Woods actress will portray Laeta, the privileged wife of a Roman dignitary who finds herself involved in the battle against Spartacus.
Australian actress Jenna Lind has been cast as Kore, a loyal slave to Simon Merrells's Marcus Crassus, while Gwendoline Taylor will play Sibyl, another slave rescued from the Romans who sets out on a quest that impresses leaders of the rebellion.
Spartacus executive Steven DeKnight recently teased that season three will be "very dirty" and "ethically muddled".
Starz renewed the epic drama series for a third run before its second season had begun airing last year.
Former Home and Away actor Todd Lasance has been cast in the series as Julius Caesar.
Watch a trailer for the second season of Spartacus below: