After several years of journalistic work, Grossmith began about 1870 as a public entertainer, with songs, recitations, and sketches. His long connection with Gilbert and Sullivan began in 1877 at the Opera Comique, London, in the comic opera The Sorcerer. Thereafter, he appeared regularly at the Opera Comique, being transferred, in 1881, with the Gilbert and Sullivan productions to the new Savoy Theatre, London.

In 1889 Grossmith left the Savoy and again set up as an entertainer, visiting all the major cities of Great Britain and the United States. He wrote an autobiography, A Society Clown (1888), and, with his brother Weedon Grossmith (1852–1919), an actor and playwright, wrote the amusing Diary of a Nobody (1892). His humorous songs and sketches exceeded 600. Both of his sons, George (1874–1935) and Lawrence Grossmith (1877–1944), were distinguished actors. George, Jr., became a well-known figure in musical comedies, entered the motion-picture industry in 1932, and wrote musical plays.