In 788, after the fall of Duke Tassilo III, Mondsee became an Imperial abbey and over the centuries acquired extensive property.

Conrad,[3] formerly a monk of Siegburg Abbey, had been abbot of Mondsee since 1127, and was extremely successful in defending and regaining the rights and possessions of the monastery, to the extent that in 1145 he was murdered by a group of nobles at Oberwang nearby.

Conrad was succeeded as abbot by Walter of Mondsee (died 17 May 1158), long remembered as a model by the community for his exemplary striving after virtue.

Under Abbot Bernhard Lidl (1727–73) and especially in connection with the celebration of the thousandth anniversary of the foundation, there was extensive re-building of the church and the monastic premises.

During that time, in 1810, the Bavarian Field Marshal Prince Karl Philipp von Wrede acquired the abandoned monastery (along with the nearby abbeys of Suben and Gleink), and used it as a castle.

In 1905, on the death of Princess Ignazia von Wrede, Mondsee passed to the Counts Almeida, whose descendants sold it in 1985.