Development and pre-production[]
On January 31, 2014, it was announced that The Walt Disney Company was developing a live-action movie based on the Disney Afternoon animated series Chip 'n Dale: Rescue Rangers with CGI special effects, similar to 20th Century Fox's Alvin & the Chipmunks film series. David Hoberman and Todd Lieberman signed on as its producers, while Robert Rugan was hired to write and direct the film. It would have followed an origin story for the Rescue Rangers. Robert Rugan debunked these claims, claiming that the project was a combination of live-action and animation, and was a direct film adaptation of the series with a slightly darker tone reminiscent to a 1940s noir film.
In May 2019, Akiva Schaffer, known for the 2007 cult classic Hot Rod, became the film's new director, replacing Rugan, while Dan Gregor and Doug Mand became its new writers and claimed that the film would follow a "meta, something self-referential and cool" take on the characters. David Hoberman and Todd Lieberman returned as its producers, and the project became a co-production between Walt Disney Pictures and Mandeville Films. Gregor and Mand had started the new script as a spiritual successor to Who Framed Roger Rabbit, taking into account the changes in animation techniques in the four decades since Roger Rabbit had been made. They wanted to keep what they felt made Roger Rabbit successful, being that the film "is not talking down to the animated characters [and] playing it real and to the top of your intelligence." Schaffer said they were further influenced by buddy cop films of the 1990s such as the Lethal Weapon series, while including more comedic elements.
Schaffer agreed to direct the film after he was sent Gregor and Mand's script; he agreed due to the film's self-referential humor, his love for both the original series and Roger Rabbit, and an interest in working on animated films. The film features cameos from several non-Disney animated properties due to Schaffer wanting the film to be "a love letter celebration of animation", similar to Roger Rabbit, and felt including only Disney characters would instead make the film "just a celebration of Disney animation". Schaffer did not want to go overboard on such cameos, going by the rule "Don’t put in a cameo unless it’s forwarding the story or putting a button on a really good laugh". Schaffer used the example of the donut cops from Wreck-It Ralph, who not only served as recognizable characters for younger audiences, but also played on the popular concept of police officers loving to eat donuts as a joke for those that had not seen the film. Non-Disney companies authorized through Disney's legal team for their characters to appear in the film after Schaffer assured them it was "not going to make fun of their characters".
Schaffer said that for the film's villain, they wanted to play on the idea of child actors that were not able to continue acting as adults through cartoon characters. Early on, the team considered using an adult version of Charlie Brown from Peanuts for the role, but eventually selected Peter Pan for easier licensing. This was compared to Bobby Driscoll, the original voice actor for Peter Pan in the 1953 film. In the years following its release, Driscoll's acting career spiraled into decline after being terminated from Disney as he reached puberty. This affected his personal life, with Driscoll becoming addicted to drugs. In early 1968, Driscoll passed away as a result of heart failure from drug abuse. Several events from this point in Driscoll's life were applied similarly to Sweet Pete's backstory. The film was heavily criticized for this, with both critics and audiences pointing out how the portrayal of Sweet Pete, with the context of Driscoll's later life in mind, came off as disrespectful and insensitive. Despite this, Schaffer had stated there was no intention to mock any specific actor in the film, and the writers had not been aware of Driscoll's history.
According to storyboard artist Simeon Wilkins, they had planned for Jar Jar Binks to feature in the convention hall scenes, but he was replaced with Ugly Sonic. Other discarded appearances included actor Chris Evans, Elliot from Pete's Dragon, Sulley and Mike from Monsters, Inc., Tick-Tock the Crocodile from Peter Pan, Sabretooth from X-Men: The Animated Series, and Mushu from Mulan.