[1] He lived in Paris in 1780–83, and in London from 1783 to 1786 as tutor in the house of the Saxon ambassador, Hans Moritz von Brühl.

In Paris and London he entered the circles of astronomers like Joseph de Lalande, Pierre-Simon Laplace and William Herschel.

At the close of the 18th century, he organised the "celestial police", a group of twenty-four astronomers, to prepare for a systematic search for the "missing planet" predicted by the Titius-Bode law between Mars and Jupiter.

[2] His principal importance was, however, as editor of three scientific journals of great value: Allgemeine Geographische Ephemeriden (4 vols., Gotha, 1798–1799), Monatliche Correspondenz zur Beförderung der Erd- und Himmels-Kunde (28 vols., Gotha, 1800–1813, from 1807 edited by Bernhard von Lindenau), and Correspondance astronomique, geographique, hydrographique, et statistique (Genoa, 1818–1826, 14 vols., and one number of the 15th, the suppression of which was instigated by the Jesuits).

In 1808, von Zach was in Marseille where he observed and explained the phenomenon of the Canigou mountain in eastern Pyrénées which can be seen twice a year from there, 250 km away, by refraction of light.