The filmmakers described the film as "a haunted-house movie with a bunch of hormonal teenagers," and cite the works of horror storyteller Stephen King and teen drama filmmaker John Hughes as an influence.
The film was going to release 13 April 2018, but the producers pushed back the date to 22 February 2019 so that it didn't conflict with Deadpool 2 (2018) and Dark Phoenix (2019). The producers took this opportunity to have parts of the film reshot so that it could be scarier, inspired by the success of recent horror films such as Get Out (2017) and It (2017).
Jon Hamm was cast to portray Nathaniel Essex / Mister Sinister, with filming for the role completed, though his role has reportedly been cut from the film as a result of an extensive reshoot process that is changing elements of the film.
Blu Hunt is Native American and Henry Zaga is Brazilian, just like their respective characters Danielle Moonstar and Roberto da Costa. However, English actors Charlie Heaton and Maisie Williams play the American Sam Guthrie and the Scottish Rahne Sinclair, and the Argentinian-English American actress Anya Taylor-Joy plays the Russian Illyana Rasputin.
The film was originally slated to come out on April 13, 2018, but was first delayed to February 19, 2019, before being pushed back again to August 2, 2019, and then it was pushed back yet again to April 3, 2020.
This film along with Deadpool 2 (2018) and Dark Phoenix (2019) were filmed around the same time with New Mutants filmed in Boston, Massachusetts, United States, Deadpool 2 in Vancouver, British Columbia, Canada and X-Men: Dark Phoenix in Montreal, Quebec, Canada.
Maisie Williams (Wolfsbane) is the third "Dr Who" actor to appear in an X-Men film, having played Ashildr. Previous actors were Ian McKellen (Magneto, the Great Intelligence) and Richard E. Grant (Dr Zander Rice, the Great Intelligence).
Maisie Williams plays Arya Stark in the HBO series Game of Thrones (2011) (TV Series). Sophie Turner whom plays Sansa Stark in the series plays Jean Grey in the X-Men films which this film is a spin-off.
In March 2019, star Maisie Williams told Rolling Stone the film is apparently stuck in corporate limbo after Disney's recently-closed acquisition of Fox, the latter of which had been licensing the Marvel Comics property since 2000's original X-Men, maintaining its own film universe ever since. As Williams states in frank fashion, "Who knows when that's gonna come out?"