Knightley is best known for her work in the films "Pride & Prejudice," "Love Actually," "Atonement" and the "Pirates of the Caribbean" franchise.
She will soon be seen in the prequel to J.M. Barrie's classic "Peter Pan," written for the small screen and directed by Nick Willing.
Syfy described Knightley's Tinker Bell as "a magical tree spirit whose strength and powers are put to the test when her colony within Neverland's treetops is endangered."
The "Neverland" cast also includes Rhys Ifans, Anna Friel, Bob Hoskins, Charles Dance, Raoul Trujillo and Charlie Rowe.
Knightley will record her role this spring, Syfy said. "Neverland" is to air on the network in December.