Prior to Warner Bros., Horn served in various positions at 20th Century Fox and at Norman Lear's television production company, Tandem Productions. Horn was also one of the founders of Castle Rock Entertainment, a company he currently oversees at Warner.
Horn sits on the board of directors of Univision.
He is a key figure of hate amongst the Harry Potter community due to his rather controversial decision to change the release date of the upcoming Harry Potter movie, less than three months before the original release date. The decision was purely financial, and Alan Horn was quoted as saying: "There were no delays. I’ve seen the movie. It is fabulous. We would have been perfectly able to have it out in November.” This resulted in a massive fan backlash. Horn made this decision against advice of his public relations team, and relations between companies such as EA, Imax, and even Entertainment Weekly (who share a parent company with WB) are fractured. In fact business analysts are speculating that this move may cost him his job in the not too distant future.