Erik Larson's acclaimed book is about two men who turned the 1893 Chicago world's fair into their playground. One of them is architect Daniel Burnham. DiCaprio would play the other character, H.H. Holmes, a serial killer masquerading as a charming doctor.
Holmes believed to be responsible for scores of murders, devising a crematorium and gas chamber near the fairgrounds and using the event to lure victims.
DiCaprio will also produce the film.