Maddux was born in San Angelo, Texas, although he spent a significant portion of his youth in Madrid, Spain, because his father was stationed there while serving in the United States Air Force. Mike and Greg Maddux were brought into this world by their parents, Dave Maddux and Linda Maddux.

Baseball was something that his father taught him to play when he was a little child. Following Greg’s return to Las Vegas, Nevada, he and his brother Mike, who also went on to have a career in professional baseball, began training with Ralph Meder, a person who had previously worked as a scout in the major leagues.

The importance of movement and position, as opposed to speed, was a fundamental tenet of Meder’s teachings. He encouraged his students to throw more gently rather than forcefully when in a tight spot.