Michael, called Hanssmichl by his father, received his first musical training in Rohrau, and in nearby Hainburg, where he was a choirboy. In 1745 he followed in brother Josephs footsteps and became a chorister in St. Stephen's Cathedral, Vienna. At St. Stephens he received rudimentary instruction in theory and practice of music. He studied violin and organ, and eventually wrote his first known work in 1754. The brilliant <i> Missa in honorem Sanctissimae Trinitatis </i>, which by far outshines brother Josef's first works of the genre.
Shortly after he left the choir-school, Michael was appointed Kapellmeister at Nagyvárad (Großwardein, Oradea) and later, in 1762, at Salzburg. The latter office he held for forty-three years, during which time he wrote over 360 compositions for the church and much instrumental music.
He was acquainted with Mozart, who had a high opinion of his work, and was the teacher of both Carl Maria von Weber and Anton Diabelli.