Due to Lübeck's recent incorporation into the French Empire, he was also able to join the local Tribunal as a "Juge suppléant" and received permission to work at the Court of Appeals in Hamburg.

During this time, he published one of his most important legal writings; Über die Fortdauer der Gültigkeit älterer Hypotheken auf Mobilien, namentlich der Hypothekwechsel, nach neuerem Recht (On the continuation of the validity of older mortgages on chattels, namely the change of mortgage, according to more recent law, 1812).

They had five children, but only one outlived him; Christian Theodor Overbeck, who also entered the legal profession and served in the Lübeck Senate.

In 1822, he was elected to the Oberappellationsgericht der vier Freien Städte (High Court of Appeal of the Four Free Cities) and began his duties on 28 May 1824.

He founded an industrial school, two kindergartens, and the "Verein zur Fürsorge für entlassene Strafgefangene" (Association for the welfare of released prisoners, 1840).