[6] Birnbaum started out in the music industry at Arista Records working under Clive Davis.
While working at film, he was appointed president of Fair Dinkum Productions, which was headed by Henry Winkler, who supervised Young Sherlock Holmes and The Sure Thing.
In August 1998, Birnbaum with Gary Barber, former vice chairman and COO of Morgan Creek Productions founded Spyglass Entertainment.
[10] On December 20, 2010, after the Metro-Goldwyn-Mayer had emerged from bankruptcy, Birnbaum and Barber became co-Chairs and co-CEOs of the studio.
[11][12] On October 3, 2012, Birnbaum announced his intention to exit his role as an MGM executive and return to "hands-on" producing.