Gassmann was born in
Brüx,
Bohemia, and was most likely trained by Johann Woborschil, the local chorus master. His father was a goldsmith who may well have opposed his son's choice of a musical career. From 1757 until 1762, he wrote an opera every year for the
carnival season in
Venice, and was also appointed choirmaster in the girls' conservatory in Venice in 1757. Many of the librettos he set were by the renowned Venetian playwright
Carlo Goldoni. In 1763 he was called to
Vienna as court
ballet composer, and was held in great affection by
Emperor Joseph II. In 1764 he was appointed chamber composer to the Emperor, and in 1772 court conductor. In 1766 Gassmann met up-and-coming young
Antonio Salieri in Venice, invited him to return with him to Vienna and taught him composition using
Johann Joseph Fux's textbook
Gradus ad Parnassum. Salieri remained in Vienna, and succeeded Gassmann as chamber composer to the Emperor on the latter's death in 1774. Another
Italian composer,
Giuseppe Bonno, succeeded Gassmann as court conductor. In 1771, Gassmann founded the
Tonkünstler-Societät (Society of Musical Artists), which was the first group in Vienna to give concerts for the general public, and for the benefit of its members' widows and orphans. He wrote his
oratorio La Betulia liberata for that purpose. In 1774, he died in
Vienna from long-term consequences of a carriage accident sustained on his final visit to Italy. Gassmann's two daughters, Anna Fuchs and
Therese Rosenbaum, were both famous singers trained by Salieri; the younger, Therese, made a particular name for herself as a
Mozart interpreter.
Charles Burney, in one of his published accounts of his many European tours surveying the musical scene, recalls, on a visit to Joseph II and his court, meeting Gassmann and finding him very forthcoming. Among the manuscripts Gassmann showed him, he reserved most of his praise for his chamber works. Burney was either not exposed to, or said nothing about, Gassmann's orchestral music.
Johann Baptist Wanhal is described by author Daniel Heartz as Gassmann's "
protégé". ==Major works==