Actress Lizzie Atherton was selected for the role of St. Bernadette in the film because of her strong resemblance to Jennifer Jones, who played Bernadette in Le chant de Bernadette (1943).
Actor Don Parker was cast for his ability to evoke Maurice Chevalier's singing style without doing an outright imitation, and for his resemblance to Gene Kelly, both of whom were inspirations for the musical number "Mimi".
Actor Sean Gallagher had long hair at the time of filming, in style something like Sideshow Bob on Les Simpson (1989). A call to the Chicago Archdiocese confirmed that priests are allowed to wear their hair any way they like, if the parishioners accept it, and so Sean sports a modest ponytail in the movie.
Among the computer generated special effects devised for the film by Paul Rosckes were St. Bernadette perched on a swing set, the city-hopping montage when Tekki arrives in Paris, and the supercharged fly ball in the baseball scene that leaves a jet trail in the summer sky.
Production Designer Carl Ulaszek and his crew constructed 17 separate interior sets for the film, including the musical number set designed by Chicago scenic artist Katherine Ross, which was inspired by the paintings of Raoul Dufy.