Pennick was born in Portland, Oregon, the son of gold miner Albert R. and Bessie (Murray) Pennick. He and his first wife, Grechin, had two children by the time he was twenty. He had a third child with his second wife, Nona Lorraine. Pennick joined the United States Marine Corps and served with the Peking Legation Guard in China in 1912 and World War I. He reenlisted in the United States Navy in September 1941, at the age of 45. He was promoted to chief warrant officer (chief photographer) in December 1942 and served in the Field Photographic Unit under Commander John Ford. Pennick was awarded the Silver Star medal for action in North Africa. He died in Manhattan Beach, California at the age of 68.