Ivan Reitman continued his work with film which had begun at McMaster where he produced and directed many short films. His first commercial film ventures were as producer of It Came From Within and Rabid. In Toronto, he produced the stage production Spellbound which evolved into The Magic Show. It played on Broadway for five years.
His off-Broadway hit The National Lampoon Show subsequently led to his film National Lampoon's Animal House, produced in 1978. The next year he directed Meatballs. Stripes and Heavy Metal were produced in 1981. Ivan Reitman's film Ghostbusters became the top-grossing comedy in motion picture history. He was producer, director and co-writer of Legal Eagles in 1986, followed later by Twins, starring Arnold Schwarzenegger and Danny DeVito. More recently, Reitman's stars have been of the canine variety, most notably Beethoven the St. Bernard. Reitman's films have been constant box office hits.

In 1983, Ivan Reitman earned a Tony nomination for directing and producing the Broadway musical Merlin. In 1985, he was awarded a Genie by the Academy of Canadian Cinema for 'Outstanding Contribution to the world of Comedy'.