Margaret Florence Greig (8 March 1855 – 30 January 1912), known by her stage name Florence St. John, was an English singer and actress of the late Victorian and Edwardian eras famous for her roles in operetta, musical burlesque, music hall, opera and, later, comic plays.
St. John began her career while still a teenager. By 1879, St. John was starring in new London productions, often creating roles, beginning with the title role in an English version of Madame Favart, which earned her critical praise. Despite occasional illnesses, she created the leading soprano roles in the light operas Olivette (1880), Barbe-bleue (1883), Nell Gwynne (1884) and Erminie (1885), among several others. In 1888, she joined the Gaiety Theatre company, playing Marguerite in the hit Victorian burlesque Faust up to Date, which toured America (1889–90), and then the British provinces. She then starred in Carmen up to Data.
In the early 1890s, St. John continued to pay at the Gaiety and also toured in the operetta Rip van Winkle. In 1892, she starred in In Town, which became a hit and ushered in the age of the Edwardian musical comedy. This was followed by the hit the burlesque Little Christopher Columbus. In 1894, she joined the D'Oyly Carte Opera Company in Mirette, created the role of Rita in The Chieftain and toured as Winifred in The Vicar of Bray. In the mid-1890s, she returned to concert singing, appearing regularly in the weekly Ballad Concerts at St James's Hall for many years. In 1897, she rejoined D'Oyly Carte, starring in the title role in the Savoy version of The Grand Duchess of Gerolstein.
In 1900, St. John made her last appearance in musical theatre as Dolores in Florodora. In 1902, she turned to "straight" theatre, starring over the next few years in several roles in London and on tour. Later, she toured the provincial variety theatres with her own company in a piece titled My Milliner's Bill, or by herself singing ballads. Her last theatrical appearance was in 1909 as Lizi in The Merry Peasant at the Strand Theatre.