"Brokeback Mountain" co-star Michelle Williams was previously announced as the female lead in the untitled film.
Production is expected to begin this summer on the film, which is being kept under tight wraps, The Hollywood Reporter said. All that is known is the movie, being written and directed by Allen, will center around a trio of young Americans living in Paris.
Krumholtz will next be seen in Emilio Estevez's production, "Bobby." Among his other film credits are "Serenity," "Ray" and "Harold & Kumar Go to White Castle."