The 32-year-old actor originally hails from Belfast, Ireland, and will portray real-life Irish Commandant Pat Quinlan in the new geopolitical thriller.
Set during the 1961 United Nations intervention in Katanga, Congo, the film will tell the story of Quinlan and 150 Irish U.N. troops, who were besieged by troops loyal to secessionist Katangese Prime Minister Moise Tshombe. The lightly-armed group held out for six days against 3,000 soldiers led by French and Belgian mercenaries before being taken prisoner.
Dornan is no stranger to a uniform, having appeared as Count Axel Fersen in Marie Antoinette (2006). He is also known for portraying Sheriff Graham/The Huntsman on ABC series Once Upon a Time, and serial killer Paul Spector on The Fall.
The actor will star as Christian Grey opposite Dakota Johnson as Anastasia Steele in Sam Taylor-Johnson's adaptation of Fifty Shades of Grey. The movie is based on E L James' bestselling novel of the same name, and opens in theaters February 13, 2015.