Screenwriter Paul Rudnick wrote the original script back in 1987 and Bette Midler was supposed to be cast for the role of Dolores. After Midler had left the project, the script underwent several re-writes by screenwriters Carrie Fisher, Eleanor Bergstein, Nancy Meyers, Jim Cash, Jack Epps Jr. and Robert Harling. As Rudnick did not consider the final draft of the movie as his own work, the pseudonym 'Joseph Howard' was chosen by him after his own suggestion for the writer's credit ('Screenplay by Goofy') had been rejected.
The Reno police station shown is actually the main post office in downtown Reno, with some (real) patrol cars parked outside for set dressing. The patrol cars were driven by officers working security on the set. The real police station in Reno didn't look as much like a police station to the film's director.
The Mother Superior dubs Deloris "Sister Mary Clarence". She states that the "Clarence" part of the moniker derives from "Saint Clarence of Concord". While there is no St. Clarence from Concord in conventional Roman Catholicism, there is a St. Clarence from Vienne who is, coincidentally, the patron Saint of prisoners.
When the marquee for the Moonlight Lounge is first shown at the beginning of the movie, the featured band name is the "Ronelles." In the scene where the nuns are going to rescue Sister Mary Clarence, the featured name of the band (with Deloris gone) is the "Leerons" (Ronelles rearranged and minus one L).
In the scene where Mary Clarence is to be shot by two of Vince's henchmen, she kneels to pray before striking each of them to run away. The chair that Mary had been tied up in is the same chair used in Star Trek: The Next Generation: Devil's Due.
While Paul Rudnick was writing the screenplay, Bette Midler (who was attached to star at the time) suggested he should go to an actual convent to do research. So he went to stay in the Regina Laudis Abbey in Bethlehem, Connecticut. The Prioress of this convent was Mother Dolores Hart, O.S.B., who as a younger woman had been an actress, singer, and dancer in such Hollywood films as the Elvis vehicle King Creole and the beach romance Where the Boys Are. Mother Hart is still the only known nun to be a voting member of the Academy of Motion Picture Arts and Sciences, and she and her fellow nuns enjoy watching her Academy screeners every year.
On June 10, 1993, Donna Douglas and her partner Curt Wilson in Associated Artists Entertainment, Inc., filed a $200 million lawsuit against Disney, Whoopi Goldberg, Bette Midler, their production companies, and Creative Artists Agency claiming the film Sister Act was plagiarized from a book A Nun in the Closet owned by the partners. Douglas and Wilson claimed that in 1985 they had developed a screenplay for the book. The lawsuit claimed that there were more than one hundred similarities and plagiarisms between the movie and the book/screenplay owned by Douglas and Wilson. The lawsuit further claimed that the developed screenplay had been submitted to Disney, Goldberg, and Midler three times during 1987 and 1988. In 1994, Douglas and Wilson declined a $1 million offer to settle the case. The judge found in favor of Walt Disney Pictures and the other defendants. Wilson stated at the time, "They would have had to copy our stuff verbatim for us to prevail."