Mary Frances Ronalds RRC DStJ (née Carter; August 23, 1839 – July 28, 1916) was an American socialite and amateur singer who is best known for her long affair with the composer Arthur Sullivan in London in the last decades of the nineteenth century and for her musical salons.
After separating from her husband, Ronalds moved with her children from New York to Paris in 1867, then to Tunis in 1869, and eventually to London in 1875. She was accepted into royal social circles and was a popular hostess. A noted beauty, she became romantically involved with Arthur Sullivan during the 1870s and continued as his companion until his death in 1900. She was much admired as a singer and became famously associated with one of Sullivan's most popular songs, "The Lost Chord".