Warren Gentaro Tonaki was born in 1917 on Maui. His parents were from Okinawa. The family moved to Oahu and were farmers in Kahaluu. After graduating from high school, Tonaki volunteered and was assigned to the 298th Hawaii National Guard, then served with the 100th Infantry Battalion in Headquarters Company.
After the war he and his two brothers started a car repair business in Kapahulu called the Kapamoi Garage.