John Douglass Wallop III was born on March 8, 1920 to John Douglass, Jr., an insurance agent, and Marjorie Wallop (maiden name Ellis).
Wallop graduated from the University of Maryland in 1942, where he served as editor of "The Old Line", a student-run literary and humor magazine.
His first novel, 1953's Night Light, the story concerns a father's search into the background of his child's murderer. Anne Brooks of the New York Herald Tribune Book Review said "created characters who are both real and colorful, and he has delved into a maniac's mind with considerable understanding." R.G. Peck wrote an article for the Chicago Sunday Tribune and said it was the "first novel that's well constructed, carefully written, and free of painful mannerisms." Al Hine of the Saturday Review said it's a "novel that is moving and tautly interesting from first page to last. Mr. Wallop writes fluently and without affectation, even when he is exploring the subcellars of bop."
He authored 13 works but is most famous for The Year the Yankees Lost the Pennant (1954), which was adapted by Wallop and George Abbott into the Tony Award-winning musical Damn Yankees.