"Du Barry Was a Lady" was adapted from a Broadway show that opened at the 46th Street Theatre on December 6, 1939 and ran for 408 performances. The opening night cast included Bert Lahr as Louis Blore, Ethel Merman as May Daly and Benny Baker, Betty Grable, Janice Carter, Adele Jergens, Tito Renaldo, Kay Sutton and Charles Walters. Much of the 'bathroom' humor (Lahr played a bathroom attendant) was not acceptable to the censors and was omitted from the movie. Later, Gypsy Rose Lee was a replacement cast member for Ethel Merman.
Marie Blake is in studio records/casting call lists for a role in the movie, but she was not seen.
Ann Sothern was supposed to have the role of May Daly (Madame Du Barry) but discovered she was pregnant. Lucille Ball was given her role instead.
Although Lucille Ball was dubbed by Martha Mears in the performance of the title song, she did her own singing for "Friendship"--a song she would reprise years later on I Love Lucy.
MGM hairstylist Sydney Guilaroff dyed Lucille Ball's hair flame red for this film, the color that she kept for the rest of her life and became her trademark.
Near the end of the movie when Red Skelton, as Louis, has an arrow stuck in his rear-end, as he pleads for it to be removed he cracks: "Hurry up, this thing is starting to pick up several radio stations already". Coincidentally, three decades later his co-star Lucille Ball went public claiming she could hear radio programs directly in her head when driving near radio transmission towers. She explained that the metal fillings in her teeth detected strong radio signals making them audible to her.
This was Zero Mostel's film debut.
When the swami (Zero Mostel) makes mock-love to Mrs. McGowan (Kay Aldridge) as if she were Hedy Lamarr, he's parodying Charles Boyer, particularly his role as Pepe le Moko in Algiers.