He started studying violin at the Prague conservatory, but soon switched to technical studies, and worked as an engineer at a sugar plant. His voice was discovered when he sang in an amateur male quartet, and after vocal training with Franz Vogl in Prague, he made his debut in 1855 in Brünn/Brno. From 1856 to 1887, he was the celebrated first tenor of the Vienna Hofoper, specializing in Mozart, but not only: in 1861, he was Vienna's first Lohengrin; other roles he created for Vienna were Manrico, Duca, Riccardo, Vasco da Gama, Erik, Stolzing, Roméo, Wilhelm Meister and Loge. When the new building of the Hofoper (the current Staatsoper) was inaugurated in 1869, he sang Don Ottavio in the very first performance there. On 10 March 1875, he was Assad in the world premiere of Goldmark's Königin von Saba. According to his own statement, he sang 2,420 evenings and 92 roles at the Vienna Hofoper. Hugo Wolf, who made his living as a music critic, criticized Walter's stage acting as clumsy.
In 1887, Walter retired from the stage, only to start a second, even more splendid career as a lieder singer – the first singer in the world to give lieder recitals (he had already started to do so when still performing opera). Until then, lieder had only been performed in mixed programs, typically in philharmonic concerts between (!) the movements of a symphony. Walter sang his lieder recitals all over Europe, particularly successful in London. He was considered the model interpreter of Schubert; Brahms (who was his personal friend) and Dvořák wrote lieder for him. Just like at the new Hofoper building, he also inaugurated both halls of the new Vienna Musikverein building in 1870 with concerts (at the Brahmssaal, his accompanist was Clara Schumann). He continued his concert career into the 20th century.
From 1882, he also taught voice in Vienna, and in that field, too, he was highly successful; among his pupils were Lula Mysz-Gmeiner, Franz Pácal and Mme. Charles Cahier.
Reference 1: Kutsch & Riemens; reference 2 (sorry for that
link, it's a terrible, radical right-wing journal, but they did once have an excellent article on Gustav Walter); reference 3; reference 4
Grammophon, Wien 1904 332i Am Meer 042097 2423h Mignon: Leb wohl, Mignon 3-42154 2424h Feldeinsamkeit 3-42155 Wiener Phonogrammarchiv, Wien 1906 237 O hör mein Lied, geliebte Maid (Eduard Walter) 237 238 Lohengrin: Nun sei bedankt 238 Note: the composer Eduard Walter is a coincidental namesake, unrelated to Gustav Walter.
I wish to thank Vladimir Efimenko for the recording (Lohengrin) and picture.