Nelson Richard DeMille was born in New York City on August 23, 1943 to Huron and Antonia (Panzera) DeMille, then moved with his parents to Long Island. He graduated from Elmont Memorial High School, where he played football and ran track.

DeMille spent three years at Hofstra University, then joined the Army where he attended Officer Candidate School and was commissioned a Lieutenant in the United States Army (1966-69). He saw action in Vietnam as an infantry platoon leader with the First Cavalry Division and was decorated with the Air Medal, Bronze Star, and the Vietnamese Cross of Gallantry. After his discharge, DeMille returned to Hofstra University where he received his bachelor's degree in Political Science and History.

He has three children, Lauren, Alexander, and James, and he and his wife reside on Long Island. DeMille's first major novel was By the Rivers of Babylon, published in 1978, and is still in print as are all his succeeding novels. He is a member of American Mensa, The Authors Guild, and is past president of the Mystery Writers of America.

He is also a member of International Thriller Writers and was chosen as ThrillerMaster of the Year 2015. He holds three honorary doctorates: Doctor of Humane Letters from Hofstra University, Doctor of Literature from Long Island University, and Doctor of Humane Letters from Dowling College.

Alex DeMille is a writer, director, and film editor. He grew up on Long Island and received a BA from Yale University and an MFA in film directing from UCLA. His films and screenplays have won many awards and fellowships, including his film The Absence which was awarded Best Film at Comic-Con in 2012. He has edited numerous commercials, shorts, and independent feature films, among them My Nephew Emmett, which was nominated for an Academy Award for Best Live Action Short in 2018. He lives in Brooklyn with his wife and daughter.