The actress - most recently seen in The CW's axed Sarah Michelle Gellar series - will join Sons in its fifth season.
Summers will play Karen Dunhill, who works alongside Tara (Maggie Siff), according to Deadline.
Her past credits include stints on Damages and Boston Legal. The English actress will also star in forthcoming TNT medical drama Monday Mornings and recently wrapped on the Hitchcock biopic with Anthony Hopkins.
Harold Perrineau (Lost) and Ashley Tisdale (Hellcats) will also appear in the new season of Sons of Anarchy.
The biker drama returns to FX on September 11 and airs on 5USA in the UK.
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Watch a promo for the new Sons of Anarchy below: