He learned piano with Vilém Kurz and Ludomir Różycki at the GTM Conservatoire. In 1910 he took up studies at Lemberg University, then the University of Vienna, from which he obtained a doctorate in musicology in 1922. For four semesters, he and Koffler were simultaneously students at the University of Vienna.
After his return to Lwów, in 1923–39 Barbag taught theory, composition, and piano classes at Lwów Music Institute (from 1931 – as the Karol Szymanowski Music Conservatoire). Though the two schools competed for students, Barbag was a friend of the PTM Conservatoire’s director Adam Sołtys. He was also a member of the board at the ISCM Lwów Branch (1930–33) and a speaker on Polish Radio Lwów. Occasionally he presented lectures at the PTM hall. His output included works for orchestra, chamber music (e.g. cello and piano sonatas), as well as songs for voice and piano. Seweryn Barbag’s music was performed at the PTM Conservatoire along with works by Józef Koffler, Roman Palester, Antoni Rudnicki, and Adam Sołtys during a 1934 ‘Concert of Lwów’s Composers’.
One of his major publications was ‘A Systematic Division of Musicology’ (Lwów, 1928). Under the Soviet occupation, Barbag found employment at the newly founded LGK Lviv State Conservatoire (1940–41). In Soviet listings he declared Polish nationality.