Production notes

Focus Features bought the rights to Patrick Ness' book in March 2014. Ness served as the film's screenwriter, with J. A. Bayona hired as director. Felicity Jones was cast on 23 April 2014, Liam Neeson was cast on 8 May, Sigourney Weaver was cast on 18 August, and Toby Kebbell was cast on 19 August. On 3 September, Ness tweeted that Lewis MacDougall had been cast in the lead role. Geraldine Chaplin joined the cast of the film on 30 September.

Principal photography began on 30 September 2014, and took place in Spain and Britain. On 9 October, filming began on location in Glossop, Preston, Lancashire (Ramsbottom), Rivington Pike (Chorley/Horwich), Blackpool Pleasure Beach, Colne Valley High School, Linthwaite, Huddersfield and Marsden, West Yorkshire. Liam Neeson, who voices the film's titular tree creature, was not on set throughout the shooting process, having completed his motion-capture performance, with MacDougall in the room, during a two-week period beforehand. Actor Tom Holland, who had previously worked with Bayona on The Impossible (2012), worked on set as the stand-in for the Monster.

A Monster Calls grossed $3.7 million in the United States and Canada and $43.5 million in other territories for a worldwide total of $47.2 million, against a production budget of $43 million. In North America, the film had its wide release alongside the opening of Underworld: Blood Wars and the wide expansions of Hidden Figures and Lion, and was initially expected to gross around $10 million from 1,523 theaters over the weekend. However, after making just $659,000 on its first day, weekend projections were lowered to $2 million, which it ended up grossing, finishing 13th at the box office. In its second weekend of wide release, the film grossed $537,262 (a drop of 74.2%), and in its third week, it made just $19,080 (a drop of 96.4%) after being pulled from all but 42 theaters, one of the biggest third week theater drops in history.

On the review aggregator website Rotten Tomatoes, 86% of 266 critics' reviews are positive, with an average rating of 7.6/10. The website's consensus reads: "A Monster Calls deftly balances dark themes and fantastical elements to deliver an engrossing and uncommonly moving entry in the crowded coming-of-age genre." On Metacritic, the film has a weighted average score of 76 out of 100 based on reviews from 40 critics, indicating "generally favorable" reviews. Audiences polled by CinemaScore gave the film an average grade of "A" on an A+ to F scale.