The 31-year-old - who played vampire Demetri in the Twilight film series - will appear in at least two episodes of the CW drama, TV Guide reports.
Bewley will play a mysterious character named Vaughn, who is described as "tough and rugged".
Camille Guaty has also won a role on the paranormal drama. The actress - best known for playing Maricruz on Fox's Prison Break - will play Caitlin, a figure from Professor Shane's (David Alpay) past.
Both Guaty and Bewley will make their The Vampire Diaries debut in the 13th episode of the show's fourth season and may recur beyond their initial two-episode stint.
Supernatural star Rick Worthy was also cast on the series last month - the 45-year-old actor will play the father of Bonnie (Kat Graham).
The Vampire Diaries airs on The CW in the US and on ITV2 in the UK.
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Watch a promo for the next Vampire Diaries below: