Constanze Mozart was musically trained and sang the soprano part in Mozart's C minor Mass at Salzburg in 1783. During their marriage she managed household responsibilities and raised their children, of whom only two survived infancy. After Mozart died in December 1791, she took an active role in securing income from his music and supporting the family beyond preserving her husband's memory.

She arranged benefit concerts, negotiated with publishers, and promoted performances. In 1795–1796 she traveled with her sister Aloysia and the pianist Anton Eberl on a concert tour that reached Hamburg, singing Mozart's works. She also published music at her own expense, including the C major Piano Concerto K.503, and sold a large collection of autograph manuscripts to Johann Anton André in 1799. These activities required decisions about ownership, publication, and access to scores at a time when Mozart's posthumous reputation was growing.

In 1809 she married Georg Nikolaus Nissen, who worked on a substantial Mozart biography with her assistance. They settled in Salzburg in 1824. After Nissen died in 1826, she helped bring the unfinished book to publication and continued to receive visitors seeking information about Mozart. She also contributed to Salzburg's musical institutions and supported plans for a Mozart monument through donations of money and materials. She died in 1842. Her work encompassed performance, publishing, and organizing musical remembrance.