He is famous for his observations of the comet he discovered (on December 13, 1743) and observed 1743 until March 1744, although this had been first discovered (on December 9) by Dirk Klinkenberg (comet 1743 Klinkenberg or Klinkenberg-De Chéseaux, C/1743 X1, 1744). De Chéseaux describes this comet in depth, which became brighter than Jupiter and at one time exhibited no less than six tails. He originally discovered another comet two years later, on August 13, 1746: Comet 1746 De Chéseaux (C/1746 P1, 1747).
In 1745 and 1746, De Chéseaux compiled a list of 21 nebulous objects, of which he had originally discovered 8 objects: IC 4665, NGC 6633, M16, M25, M35 (this one might have seen before by John Bevis in England), M71, M4, and M17. Moreover, he independently re-discovered M6, NGC 6231 and M22 (No. 17). De Chéseaux sent this list to his grandfather, Reaumur, in Paris, and it was read by Reaumur at a meeting of the French Academy of Sciences on August 6, 1746 and mentioned by Le Gentil (1759), but then stayed unpublished and more or less forgotten until Guillaume Bigourdan recovered and published it within a larger paper in 1884 (Bigourdan 1892).
De Chéseaux was among the first to formulate Olbers' paradox.
De Chéseaux did not grow very old; he died on November 30, 1751 at age of only 33.