He was born Orest Rusnak, of Ukranian origin. In World War I he served as an officer in the Austro-Hungarian army. He began voice studies in 1918 with Eugen Fuchs in Prague. His debut as Rodolfo in La Bohème took place in 1923 at Olmütz; he then sang in Königsberg (1924-26) and Stettin (1926-27). He studied again with Jacques Stückgold in Paris and with Lari in Milan. From 1928-1930 he sang in Chemnitz and the next two years in Graz. In 1931 he became a member of the Munich State Opera where he sang under the name Rudolf Gerlach-Rusnak. He stayed in Munich until 1937. Later he made guest appearances in Vienna and elsewhere. From 1941-1942 he sang in Bremen, then in Insbruck. Even after developing heart problems, he sang and toured Canada and the USA in 1957. Gerlach-Rusnak had a seraphical tenor voice of a rare timbre and with unusual extension at the top. His best roles were perhaps Edgardo in Lucia di Lammermoor, Il Duca in Rigoletto, Chapelou in Le Postillon de Lonjumeau, Narraboth in Salome and Matteo in Arabella. He recorded for HMV and his last recordings were made in 1957 in the USA.