Holdefer graduated from Loyola University in Baltimore, Maryland in 1953 and earned his doctorate in medicine in 1957 from the University of Maryland. He served his second residency in thoracic and cardiovascular surgery at UAB and joined the faculty in 1967. Through most of his career Holdefer worked as an emergency room doctor. In 1988 he joined MEDjet and flew over 300 missions.
Heldefer wrote a memoir centered on his experiences with MEDjet entitled Just Call Me Dr. Bill.
Holdefer died in 2009 and was survived by his wife, Helen, six children, 12 grandchildren and 1 great-grandchild.