Renzetti has been writer, director, and storyboard artist for several Cartoon Network shows, including "2 Stupid Dogs", "Dexter's Laboratory", "The Powerpuff Girls", "Samurai Jack", and "Foster's Home for Imaginary Friends." He won an Emmy award in 2009 for his work on Foster's. During the mid-1990s, he created "Mina and the Count", a series of animated shorts that premiered on the "What a Cartoon!" show then later aired for a short time on the similar anthology series "Oh Yeah! Cartoons". In 1999, he made the short "My Neighbor Was a Teenage Robot", which also debuted on "Oh Yeah! Cartoons"; in 2003, "My Life as a Teenage Robot", based on the short, debuted on Nickelodeon. In April 2008, he started work on Cartoon Network's "The Cartoonstitute" project as supervising producer.