He will star opposite Swedish actress Alicia Vikander in the BBC Films feature being produced by David Heyman, directed by James Kent, with a screenplay written by Juliette Towhidi.
Alicia is portraying Vera Brittain (a role previously rumoured to have Saoirse Ronan attached) and Kit will play her fiance Roland.
Based on the classic First world war memoir, Testament of Youth is the true story of one young woman’s struggle to survive the horrors of war, which robbed her of everyone and everything she held dear, but was ultimately unable to break her extraordinary spirit.
Kit Harington (represented in the UK by United Agents) landed the Game of Thrones role soon after graduating from Central drama school. He will next be seen starring in Pompeii due out this spring. He previously worked with Alicia Vikander on Seventh Son, a fantasy film that is scheduled for release in February 2015.
Vera Brittain, irrepressible, intelligent and free minded, overcomes the prejudices of her family and hometown to win a scholarship to Oxford. With everything to live for, she falls in love with her brother’s close friend Roland Leighton as they go to university to pursue their literary dreams. But the First World War is looming and as the boys leave for the front Vera realises she cannot sit idly by as her peers fight for their country, so volunteers as a nurse. She works tirelessly, experiencing all the horrors of war, as one by one her fiancé, her brother and their closest friends are all killed and the pillars of her world shattered. But, an indefatigable spirit, Vera endures, rediscovers love and returns to Oxford, irrevocably changed, yet determined to create a world in which such a war can never take place again.
Testament of Youth was last adapted as a BBC TV mini-series in the late 1970s starring Cheryl Campbell.
The new film is due to start shooting in March.