Haaga came to the attention of the horror community after co-starring in the Troma film Terror Firmer. He went on to fill the role of screenwriter as well as assistant director on the fourth film in the Toxic Avenger series, Citizen Toxie: The Toxic Avenger IV. Due to also playing the leader of the Diaper Mafia in this film, he was forced to direct many scenes in the film while wearing a baby bonnet and an adult diaper. He relates many of these experiences as co-author of the book Make Your Own Damn Movie! written with Lloyd Kaufman of Troma.
Haaga works in independent film and has stated that he likes the advances made in digital cinematography.