Harris D. Riley, Jr., was born in Clarksdale, MS, and grew up in Tupelo, MS. He attended Vanderbilt University, receiving his B.A. in 1944 and his M.D. in 1948. After internships at the Baltimore City and Johns Hopkins Hospitals, Dr. Riley completed residency training in pediatrics at the Babies and Children's Hospital, Case Western Reserve University, and at Vanderbilt University Hospital. Thereafter, he undertook fellowhip training in pediatric infectious diseases at Vanderbilt.

Dr. Riley, better known as "Pete," served in the U.S. Air Force Medical Service during the Korean War. He served as an instructor in pediatrics at Vanderbilt from 1953-1957. In 1958, he became Professor of Pediatrics and Head of the Department of Pediatrics at the University of Oklahoma College of Medicine. He remained at the University of Oklahoma until 1991. In 1991, he was appointed Professor of Pediatrics at Vanderbilt University, where he worked closely with Dr. Roscoe R. Robinson on special projects.

Dr. Riley is a prolific writer on medical and historical topics. He is an expert on Civil War medicine and a collector of books about the Civil War. He presented his Civil War book collection to the Heard Library at Vanderbilt University in 2005.