Inspired by an urban legend that co-writer Steve Bing heard as a teenager, about a pair of Boston college students on break in Australia. While driving through the Outback, they accidentally hit a kangaroo with their Land Rover. Thinking they had killed it, they got out and placed the driver's Boston Red Sox jacket on the kangaroo to take a picture before moving on. However, the kangaroo was merely unconscious, and awoke in the midst of the photo-taking. It broke free and took off across the Outback, still wearing the Sox jacket...along with the keys to the Land Rover in the pocket.
The film hit #1 in its opening weekend, despite dismal reviews. This is a famous example of false advertising. Many parents said they felt deceived by the film. The Kangaroo Jack character is front and center in all of the posters and commercials, even though he's not the main character, he only speaks in a brief dream sequence and he's only in the movie for about five minutes. Asked if it wasn't misleading to run TV spots with a talking kangaroo when the kangaroo barely talks in the actual film, former Warner Bros. marketing chief Dawn Taubin explained: "There's clearly a lot of kangaroo in the movie. And our exit polls indicated very strongly that a large percentage of the audience were highly satisfied with the movie.
Filmed in spring 2001 in Sydney, Australia, under the working title "Down and Under". This was written and shot as a hard-R mob comedy, featuring adult language, sexual themes, on-screen murders, nudity (including full frontal nudity from Jerry O'Connell and rear nudity from Anthony Anderson) and a kangaroo that didn't talk. When Warner Bros. initially test screened this cut of the film, it scored poorly. The test audience was told they would be seeing a movie "about a kangaroo with a jacket on". With that, they assumed it was a kids movie about a talking kangaroo that they can bring their kids to, only to see an adult crime comedy full of cursing, violence and sexual humor/nudity. Around this time, another kids' movie where the titular animals only speak in one scene and the entire scene is merely a dream was about to come out, which was Disney's Snow Dogs (2002). Inspired by the ad campaign for that film, producer Jerry Bruckheimer decided to make the kangaroo talk, change the name to "Kangaroo Jack" and edit it as a PG family film. Warner Bros. ended up spending an extra $10 million for two weeks of additional shooting (including the scene where Charlie dreams about Jackie Legs talking and rapping), and to replace its animatronic kangaroos with CG kangaroos. In the summer of 2002, after the new effects were completed, Warner Bros. had a new "Kangaroo Jack" test screening and it went through the roof, it was the biggest change in test screening numbers in Warner Bros.' history.
The film is regarded as one of the worst films of the 2000s. In fact, when the film came out, the reviews were so bad that producer Jerry Bruckheimer actually asked Jerry O'Connell to never read any of the reviews. O'Connell listened to the producer's suggestion and did not find out the film's Rotten 8% approval score until a Vice interview in 2017, to which O'Connell simply responded, "Yikes."
Producer Jerry Bruckheimer brought in scores of writers to punch up the script. Participants included such well-known comedy hands as Lowell Ganz & Babaloo Mandel, Peter Farrelly & Bobby Farrelly, Gary Ross and E. Max Frye.