The actress will reunite with her Buffy co-star Sarah Michelle Gellar in the show's tenth episode, according to TV Line.
She will play Mary Curtis, a stripper who works as an informant for Agent Machado (Nestor Carbonell).
Benson played Tara on Buffy the Vampire Slayer from 1999 to 2002. Her additional credits include guest roles on Supernatural, Grey's Anatomy and Private Practice.
Veronica Mars star Jason Dohring and All My Children's Billy Miller have also signed up for roles on Ringer.
The show continues on Tuesdays at 9/8c on The CW. Sky Living airs the show on Thursdays at 8pm in the UK.
> Ringer: 'It's Gonna Kill Me, But I'll Do It' recap
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Watch a promo for the next episode of Ringer below: