Reitman was born in Komárno, Czechoslovakia, on October 27, 1946, the son of Klara and Ladislav “Leslie” Reitman. His parents were Jewish; his mother survived the Auschwitz concentration camp and his father was an underground resistance fighter. His family came to Canada as refugees in 1950. Reitman attended Oakwood Collegiate in Toronto and was a member of the Twintone Four singing group.

Reitman attended McMaster University, receiving a Bachelor of Music in 1969. At McMaster he produced and directed many short films.

Reitman’s first commercial film ventures were as producer of two films for director David Cronenberg, Shivers (1975) and Rabid (1977). His big break came when he produced National Lampoon’s Animal House in 1978 and directed Meatballs in 1979. From there, he directed and produced a number of comedies including Stripes (1981), Ghostbusters (1984), Legal Eagles (1986), Twins (1988), Ghostbusters II (1989), Kindergarten Cop (1990), Dave (1993), Junior (1994), Six Days, Seven Nights (1998), Evolution (2001), My Super Ex-Girlfriend (2006), and No Strings Attached (2011).

In April 1996, it was reported that Reitman was attached to produce, and possibly direct, a Wonder Woman film. However, three years later, he passed the project on to writer Jon Cohen and left for unknown reasons.

In 2007, Reitman was inducted into Canada’s Walk of Fame. Reitman founded The Montecito Picture Company, a film production company located just south of Santa Barbara, founded in 2000.

In March 2007, New York magazine, citing no sources, stated that Sony Pictures Entertainment wanted to replace Reitman on Ghostbusters III with a younger director, but that Reitman’s original contract precluded this. In early 2010, it appeared as if Reitman would direct the film, but in September 2014, after Harold Ramis’ death, Paul Feig was officially set to direct a new film, which was released in 2016 as a reboot of the franchise. In mid-January 2019, news of Ghostbusters: Afterlife came through with Ivan’s son Jason taking over as co-writer and director. According to Ernie Hudson, “Ivan Reitman is there and everybody is in” and that Dan Aykroyd was the one who helped do story treatment with Sony.

He next produced the comedy I Love You, Man (2009), starring Paul Rudd and Jason Segel. Also in 2009, he produced the Academy Award-nominated film, Up in the Air, directed by his son Jason Reitman. Later, Reitman had planned to direct the erotic thriller Chloe (2009), but he couldn’t attract the cast he wanted; so Reitman decided to only serve as a producer and asked Atom Egoyan to direct the film. Chloe has since enjoyed commercial success and became Egoyan’s biggest moneymaker ever.

In 2009, he was made an Officer of the Order of Canada “for his contributions as a director and producer, and for his promotion of the Canadian film and television industries”.

In April 2011 he received the Mayor’s Prize at his native city of Komárno, Slovakia.

Reitman co-produced the biographical film Hitchcock, released on November 23, 2012. Reitman also directed the 2014 sports drama Draft Day, starring Kevin Costner.

In March 2012, it was reported that a sequel of Twins, entitled Triplets, was in the works, and that Reitman will co-produce the film. A release date wasn’t given since the announcement.

In 2013, it was revealed that Reitman had plans to make a sequel to Evolution, but plans for a sequel never materialized.

In May 2016, Reitman revealed that he was in talks with Warner Bros. chairman Bob Daly about his possible involvement in Space Jam: A New Legacy, the sequel of Space Jam. A month later, it was reported that Reitman will produce the upcoming animated series Ghostbusters: Ecto Force. Reitman will also produce and co-direct an animated Ghostbusters film alongside Fletcher Moules.