Earlier this week, Heat Vision broke that Maggie Q, Zoe Kravitz and Ansel Elgort sealed deals to join the cast.

Neil Burger is directing from a screenplay by Vanessa Taylor. Evan Daugherty penned an earlier draft.

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James, whose credits include Underworld: Awakenings, is known for a short but memorable stint on Downton Abbey as Lady Mary's (Michelle Dockery) lover.

Divergent is set in a future world where people are divided into distinct factions based on their personalities. Tris Prior (Woodley) is warned she is "divergent" and will never fit into any one group. When she discovers a conspiracy to destroy all Divergents, she must find out what makes being Divergent so dangerous before it's too late. A man with a mysterious past, Four, is Tris’ intense yet charismatic instructor and one of the leaders of the Dauntless faction.

Principal photography begins in April in Chicago.

Doug Wick and Lucy Fisher (The Great Gatsby) are producing the project via their Red Wagon banner alongside Pouya Shahbazian. Red Wagon’s Rachel Shane is executive producing.

Summit will release the film theatrically in North America in The Hunger Games' slot on March 21, 2014.

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In a statement, Rob Friedman and Patrick Wachsberger, co-chairmen of Lionsgate Motion Picture Group, said: “Theo is not only an incredibly talented actor, he is also whom we envisioned as Four when reading Veronica’s novel, which has taken the world by storm. As we continue to develop the film, the studio remains committed to providing fans with a movie adaptation that stays as true to the book as possible, and we are confident that we have done so with our selection of Shailene and Theo in the leading roles."

Added Erik Feig, Lionsgate Motion Picture Group’s president of production: “We took our time to find the right actor to fill the role of Four, and Theo is definitely the perfect fit. Veronica has crafted a truly iconic character in Four, and we cannot wait to begin production and bring him and this story to life for millions of fans around the world.”

James is repped by WME and Markham, Froggatt & Irwin.

Email: Tatiana.Siegel@THR.com, Twitter: @TatianaSiegel27