From 1790 to 1796 Mrongovius taught Polish and Greek at the Collegium Fridericianum. In 1796 he married Wilhelmina Luise Paarmann.
Mrongovius spent from 1790 to 1796 instructing in Polish and Greek at the Collegium Fridericianum, before marrying Wilhelmina Luise Paarmann in 1796.