Like many other distinguished German jurists, pari passu with his professorial activity, Simson followed the judicial branch of the legal profession, and, passing rapidly through the subordinate stages of auscultator and assessor, became adviser (Rath) to the Landgericht in 1846.

In Berlin on 3 April 1849, Simson appeared in his capacity of president at the head of a deputation of the Frankfurt Parliament to announce to King Frederick William IV his election as German Emperor by the representatives of the people.

The king, either apprehensive of a rupture with the Austrian Empire, or fearing detriment to the prerogatives of the Prussian crown should he accept this dignity at the hands of a democracy, refused the offer.

Simson, bitterly disappointed at the outcome of his mission, resigned his seat in the Frankfurt Parliament, but in the summer of the same year was elected deputy for Königsberg in the popular chamber of the Prussian Landtag.

On 18 December 1870, Simson arrived at the head of a deputation in the German headquarters at Versailles to offer the imperial crown to the king of Prussia in the name of the newly elected Reichstag.