Samuel L. Jackson said of working with James McAvoy on the movie, "As good as I like to think I am or what I do and how I do it, watching somebody transform characters in front of your eyes and have an argument with four different people is pretty amazing."
Director M. Night Shyamalan was able to incorporate unseen footage filmed for but deleted from Incassable (2000) into this movie, for the first flashback scene between the younger versions of David and Joseph, as well as a flashback to Mr. Glass as a young boy breaking his arm at the fair.
Although Disney owns the rights to Incassable (2000), director M. Night Shyamalan retained the rights to any potential sequels, so that the studio could not make one without his involvement. Such was his desire for creative control that he co-financed this film by mortgaging his house.
Director M. Night Shyamalan talked about the importance of colors in this movie, saying, "I chose green for David Dunn because psychologically, it is associated with life giving properties. David is the protector of life. I chose ochre or mustard for The Beast because this color is associated with religious ceremonies, Hindu and Buddhist. A monk's robe. I see The Beast as an evangelist, a preacher who wants to help save 'The Broken.' Finally, I chose purple for Mr. Glass because this color has been associated with royalty, majestic qualities. Elijah sees himself as important, a main character of comics."
Director M. Night Shyamalan said that the original cut of the film had a run time of nearly three and a half hours. He "trimmed it up a bit" by cutting three of Kevin Crumb's 23 personalities out of the film.
M. Night Shyamalan: Jai, the man talking to Joseph in the security shop. Shyamalan played the same character in Split (2016), and in this film, he confirms that he was also the Stadium Drug Dealer briefly interrogated by David Dunn in Incassable (2000).