Eventually Marianne married a wealthy magistrate, Johann Baptist Franz von Berchtold zu Sonnenburg (23 August, 1783), and settled with him in St. Gilgen, a village in Austria about 29 km east of the Mozart family home in Salzburg. Berchtold was twice a widower and had five children from his two previous marriages, whom Marianne helped raise. She also bore three children of her own: Leopold Alois Pantaleon (1785–1840), Jeanette (1789–1805) and Maria Babette (1790–1791).
An unusual episode in Marianne's life occurred when she gave birth (27 July 1785) to her first child, a son who was named Leopold after his grandfather. Marianne had traveled from her home in St. Gilgen to Salzburg for the birth. When she returned to St. Gilgen, she left her infant in the care of her father and his servants. The elder Leopold stated (by a letter that preceded Marianne back to St. Gilgen) that he would prefer to raise the child for the first few months himself. In 1786 he extended the arrangement to an indefinite term. Leopold continued to care for his grandson, taking delight in his progress (toilet training, speech, and so on), and commencing with the very beginnings of musical training. Marianne saw her son on occasional visits, but in general was not involved in his care. The arrangement continued until the death of Marianne's father, Leopold, on 28 May 1787.
Marianne's husband died in 1801. She returned to Salzburg,accompanied by her two living children and four stepchildren, and worked as a music teacher.