 Monckton soon became a regular composer (and sometimes lyricist) of songs for the very successful series of frothy musical comedies performed at London's Gaiety Theatre, under the management of George Edwardes, which premiered throughout the 1890s and into the first decade of the 20th Century.Among others, he wrote half of the music for Arthur Roberts's burlesque "Claude Du-Val" (1894) and supplemented Ivan Caryll's score for the hit musical "The Shop Girl" in the same year, with such successful pieces as George Grossmith, Jr.'s "Beautiful Bountiful Bertie" and "Brown of Colorado" (with Adrian Ross).He then added popular tunes to Caryll's scores for "The Circus Girl" in 1896 ("A Simple Little String" and "The Way to Treat a Lady") and "A Runaway Girl" in 1898 ("Soldiers in the Park", "Society", "The Sly Cigarette", "The Boy Guessed Right" and "Not the Sort of Girl I Care About").