His shop became the second-largest apothecary in Berlin, and the most productive artisanal chemical research center in Europe.

[2] In 1771, Klaproth returned to Berlin to work for Valentin Rose the Elder as manager of his business.

[1] An exact and conscientious worker, Klaproth did much to improve and systematise the processes of analytical chemistry and mineralogy.

[11][4] Klaproth was the first to discover uranium, identifying it first in torbernite but doing the majority of his research on it with the mineral pitchblende.

[8] Klaproth independently discovered cerium (1803), a rare earth element, around the same time as Jöns Jacob Berzelius and Wilhelm Hisinger, in the winter of 1803.

[16]: 497 Klaproth verified the presence of an oxide of an unknown element in the ore rutile from Hungary in 1795.

[18] Klaproth clarified the composition of numerous substances until then imperfectly known, including compounds of then newly recognised elements tellurium, strontium and chromium.

[8][19][20][2] The existence of tellurium was first suggested in 1783 by Franz-Joseph Mueller von Reichenstein, an Austrian mining engineer who was examining Transylvanian gold samples.

[26] Klaproth, Thomas Charles Hope, and Richard Kirwan independently studied and reported on the properties of strontianite, the preparation of compounds of strontium, and their differentiation from those of barium.

[27][28] Louis Nicolas Vauquelin reported the existence of a new element common to emerald and beryl in 1798, and suggested that it be named "glucine".

Klaproth confirmed the presence of a new element, and became involved in a lengthy and ongoing debate over its name by suggesting "beryllia".

[23][8][16]: 348–352 [24][29] Klaproth published extensively, collecting over 200 papers by himself in Beiträge zur chemischen Kenntnis der Mineralkörper (5 vols., 1795–1810) and Chemische Abhandlungen gemischten Inhalts (1815).

[31] In 1823, botanist Carl Sigismund Kunth published a genus of flowering plants (belonging to the family Loasaceae), from Central America as Klaprothia in his honour.