Mirams joined the New Zealand Army at the outbreak of World War II, working as a war correspondent and cameraman throughout the duration of the war, which saw him travel with the New Zealand Division throughout Italy and the Middle East. Following the end of the war, he travelled to Japan where he filmed a documentary about the war crimes trials that were held there. He then joined the New Zealand National Film Unit as a director and cameraman and later became the Movietone News representative for New Zealand.