Lev Berg graduated from the Moscow University in 1898. Between 1903 and 1914, he worked in the Museum of Zoology in Saint Petersburg. He was one of the founders of the Geographical Institute, now a Faculty of Geography of the Saint Petersburg University.

Berg studied and determined the depth of the lakes of Central Asia, including Balkhash and Issyk Kul. He developed Dokuchaev's doctrine of natural zones, which became one of the foundations of the Soviet biology. Among his pioneering monographs on climatology were "Climate and Life" (1922) and "Foundations of Climatology" (1928).

During his lifetime, Berg was a towering presence in the science of ichthyology. In 1916, he published four volumes of the study of Fishes of Russia. The fourth edition was issued in 1949 as Freshwater Fishes of the Soviet Union and Adjacent Countries and won him the Stalin Prize. He was said to have discovered the symbiotic relationship between lampreys and salmon. Berg's name is featured in the Latin appellations of more than 60 species of plants and animals.

In the West, Berg is best known as the author of the controversial macroevolution theory of Nomogenesis (Berg, L. S. Nomogenes ili evolutsia na osnove zakonomernostey. Trudy geograficheskogo instituta. T. 1. Petersburg: Gos. Izd 1922).