While a student at the university in his native city of Dorpat (now Tartu in Estonia), Lenz accompanied a voyage around the world as a geophysicist. Soon after his return he started teaching at the University of St. Petersburg, where he became professor in 1836.

Lenz worked on electrical conduction and electromagnetism. In 1833 he reported investigations into the way electrical resistance changes with temperature, showing that an increase in temperature increases the resistance (for a metal). He is best-known for Lenz's law, which he discovered in 1834 while investigating magnetic induction. It states that the current induced by a change flows so as to oppose the effect producing the change. Lenz's law is a consequence of the, more general, law of conservation of energy.