The project - currently at pilot stage - is written by Craig Silverstein (Nikita) and directed by Rupert Wyatt (Rise of the Planet of the Apes).
Gorman will play Major Hewlett in the spy drama, according to Deadline.
Turn - set in the summer of 1778 - tells the story of an unlikely spy ring formed by a New York farmer and his childhood friends who fight for American independence.
38-year-old Gorman - best known for playing Owen Harper on sci-fi drama Torchwood - has also appeared on film in 2010 comedy Cemetery Junction and superhero blockbuster The Dark Knight Rises.
He recently made his US television debut on ABC series Revenge and will next be seen in Guillermo del Toro's Pacific Rim.
Gorman's former Torchwood co-star John Barrowman currently appears on The CW's Arrow, while Eve Myles - who played Gwen Cooper on the show - is set to star in new BBC drama Frankie.
> Torchwood hasn't been cancelled, says Russell T Davies