Attended Sandhurst Military Academy and served for two years in Malta in 1930-32 as a platoon commander in the Highland Light Infantry. He then began a career in film acting in Hollywood but at the outbreak of World War II, he re-joined the Army. He started as a lieutenant in the Rifle Brigade, volunteered for commando training and found himself in a forward reconnaissance regiment called "Phantom".

2nd. Lt. D. Niven, Highland Light Infantry

He did act in two propaganda films during the war, The First of the Few (1942) and The Way Ahead (aka The Immortal Battalion, 1944). During his war service his batman was Private Peter Ustinov (actually, this was only a posting to keep the two together to work on the script for The Way Ahead, as Ustinov was barely able to keep his own kit in order). On his return to Hollywood after the war, Lieutenant Colonel Niven was made a Legionnaire of the Order of Merit (the highest American order that can be earned by a non-citizen) by General Eisenhower.

Niven was almost totally silent about his war experiences. He said once: "I will, however, tell you just one thing about the war, my first story and my last. I was asked by some American friends to search out the grave of their son near Bastogne. I found it where they told me I would, but it was among 27,000 others, and I told myself that here, Niven, were 27,000 reasons why you should keep your mouth shut after the war."

His war/historical action film credits include: The Real Glory, The Dawn Patrol, The Charge of the Light Brigade, First of the Few, The Way Ahead, The Guns of Navarone, 55 Days at Peking, The Captive City, The Best of Enemies, Sea Wolves, Last Charge ofthe Calcutta Light Horse.