Weitz began his film career as a co-writer on the animated film "Antz" (1998). He followed this with work on various sitcoms such as "Off Centre" and the 1998 revival of the 1977 TV series "Fantasy Island". In 1999, he and Paul directed and produced "American Pie", which was written by Adam Herz, and became a major box office success. Weitz returned as executive producer on the film's two theatrical sequels. In 2001, along with his brother, he co-directed his second film, the Chris Rock comedy "Down to Earth".