The Spartacus actor will play a dealer who used to sell drugs to Sherlock (Johnny Lee Miller), it was revealed at the TCA press tour.
The 50-year-old Scottish actor's recent US television roles have included the part of Batiatus in Starz series Spartacus and Rutger Simon in the final season of Damages.
He is also knowing for appearing in the series Rebus and played the lead role in Sky1 cop spoof A Touch of Cloth, while his film credits include Four Weddings and a Funeral, 1998's Sliding Doors and the Mummy franchise.
Elementary continues on Thursday at 10/9c on CBS and returns to Sky Living in the UK in February.
The show has been granted the coveted post-Super Bowl slot by CBS - a special episode will follow the sporting event on Sunday, February 3, 2013.
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Watch a clip from Elementary below: