The spy drama - from Homeland's Howard Gordon - will star Sean Bean as a CIA agent with the uncanny ability to assume different personas.
Harris will play Yates, the director of the CIA Task Force that sends Bean's character Martin Odum back undercover, according to Deadline.
The 47-year-old actor is perhaps best known for playing Eugene Young on legal drama The Practice between 1997 and 2004, and recently starred as Detective Isaiah 'Bird' Freeman on short-lived NBC drama Awake.
Amber Valletta (Revenge) will also appear in the Legends pilot as Martin's ex-wife and the mother of his young son, while Napoleon Dynamite actress Tina Majorino will play a rookie CIA field agent and Rob Mayes (90210, John Dies at the End) has been cast as an ex-Special Ops agent turned CIA operative.
Legends is based on the 2005 novel by Robert Littell. Brendan Fraser was originally cast in the lead role, but later dropped out following a creative disagreement with exec producer Gordon.
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