Mitscherlich, who was born at Neuende in Germany, studied oriental languages at Heidelberg and Berlin. He then turned to the study of medicine at Göttingen in 1817, where he became interested in crystallography. For two years he worked with Jöns Berzelius in Stockholm, returning to Berlin in 1821, where he was appointed to the chair of chemistry.

While working on arsenates and phosphates, Mitscherlich realized that substances of a similar composition often have the same crystalline form, and from this he formulated, in 1819, his law of isomorphism. This was in opposition to the orthodox view of René Haüy that each substance has a distinctive crystalline form. Despite Haüy's rejection of the law, Berzelius accepted it and was quick to spot its significance, for if the composition of a substance X is known, and it is also known that X has a similarity of crystalline form with Y, then Y's composition can be derived. Thus knowing the composition of sulfur trioxide as SO₃, and that it has a similar form to ‘chromic acid’, Berzelius was able to give this compound the composition CrO₃. Using this technique Berzelius produced his revised table of atomic weights in 1826.

Mitscherlich also discovered selenic acid (1827), named benzene, and showed, in 1834, that if benzene reacts with nitric acid it forms nitrobenzene.