Kuhn was educated at the university in his native city of Vienna and then at Munich, where he obtained his PhD in 1922. He worked at the Federal Institute of Technology in Zurich from 1926 to 1929, when he moved to the University of Heidelberg to serve as professor of chemistry and, from 1950, as professor of biochemistry.

Like Paul Karrer, Kuhn worked mainly on the chemistry of plant pigments and vitamins, repeating many of Karrer's results. In particular Kuhn, independently of Karrer, worked out the structures of vitamins A and B₂, and, in 1938, he also synthesized vitamin B₆.

For his work on carotenoids and vitamins Kuhn was awarded the Nobel Prize for chemistry in 1938, the year following the same award to Karrer. Hitler however objected to the award and Kuhn was forced to wait until the end of World War II before he was allowed to receive the prize.