[a] In 1790 Tilesius began studies of natural sciences and medicine at the University of Leipzig, and at the same time took drawing lessons from Adam Friedrich Oeser at the art academy in the Pleissenburg.

He participated as a ship's doctor, marine biologist and expedition artist on the frigate Nadezhda in the first Russian circumnavigation of the globe during 1803-1806 under Adam Johann von Krusenstern.

The Nadezhda departed from Kronstadt on the Baltic Sea, with Tlesius joining the expedition at Copenhagen; included among his baggage were a violin and viola, which he played on the voyage.

Honors Tilesius received on his return included being made a knight in the Order of St. Vladimir, corresponding membership of the Imperial Academy of Sciences, and a lifetime pension of 300 rubles per year.

He continued to lecture and publish on zoological, medical and ethnographic subjects, and attained membership in a number of scientific societies across Europe and in the United States, but did not obtain another academic position.