Slapoffski toured the British provinces as a violin soloist and played in the orchestra for the first London production of Offenbach's Madame Favart at the Strand Theatre (1879) before a period as first violin in the orchestra at the Opera Comique in London. Slapoffski married Charlotte Barrett (1863–1896) on 4 October 1881 at All Saints Church in Oxford, where the first two of their children were born. In total they were to have eight children: Adolph William Frank Prosper Slapoffski (1882–1902); Anne Hunter Slapoffski (1884–1964); Charlotte "Lottie" Douglas Slapoffski (1885–1969); Gustave Slapoffski, Jnr (1887–1932); Robert Slapoffski (1888–1914); Lola Slapoffski (born 1892); Claude Leo Slapoffski (1894–1961), who served in the Australian Army during World War I; and Mary Slapoffski (1896–1933). Nicknamed "Slap", Slapoffski was appointed musical director at the Princess Theatre in Manchester before becoming orchestra leader and first violin with the Carl Rosa Opera Company, for whom he was also assistant conductor, taking part in British tours of Jeanie Deans (1894); The Flying Dutchman (1895); Carmen (1895) and Tannhäuser (1896). A Freemason, in 1894 Slapoffski joined the Lodge of Emulation No. 1505. His right arm was virtually paralysed from his career as a violinist necessitating his conducting with his left. In early 1897 he was still playing as well as conducting for Carl Rosa in a season at the Garrick Theatre when they presented Godard's La vivandière, Roméo et Juliette, Faust, Tannhäuser, Lohengrin, Mignon and Die Meistersinger among other works. By October 1897 Slapoffski was principal conductor during Carl Rosa's short season at the Royal Opera House that included The Bohemian Girl. In 1899 he conducted for Carl Rosa's British tour of Faust, Il trovatore, The Bohemian Girl and Three Musketeers. Following on from this success, in 1900 the conductor Hans Richter suggested Slapoffski to the Australian theatre producer George Musgrove as a suitable musical director for a forthcoming season of opera in Australia. Move to Australia Slapoffski went to Australia with his second wife, the soprano Elizabeth "Lillian" Frances Williams (c. 1877–1952), who had appeared with Carl Rosa. The couple would stay in Australia for the rest of their lives. During that 1900 season Slapoffski conducted performances in Melbourne, Sydney, Adelaide and New Zealand including the Australian premières of Tannhäuser, Lohengrin and The Flying Dutchman. His wife sang Elsa in Lohengrin and Marguerite in Faust, to critical acclaim. In May 1901 Slapoffski conducted a concert to celebrate the inaugural