Born to Czech and Croatian parents in Vukovar, Croatioa, Ruzicka attended the classics-program secondary school in Osijek. Then he went to the Technische Hochschule at Karlsruhe, Germany, where he began his chemical studies in 1906. He started his doctoral work on ketenes with Hermann Staudinger, who was only a couple of years older than Ruzicka.
Then he moved to Switzerland. While filling his teaching position, in 1918 he came into contact with the chemistry of oil essences (volatile oils) in a perfume factory in Geneva. In 1921 his most fruitful work began by establishing the structure and synthesis of alicyclic ketones. He also showed that the carbon skeletons of terpenes and many other large organic molecules are constructed from multiple units of isoprene.
Ruzicka formulated a rule of thumb called the "isoprene rule" and established the connection characterizing isoprene units. During his comprehensive experiments, he set up various groups of the terpenes. By conducting research on the naturally occurring musk perfumes, civetone and muscone, he provided the fragrance industry with valuable raw materials.
In 1926 he took over the organic chemistry chair at the Utrecht University in the Netherlands. He remained there for a short period, and then returned to Switzerland, which was superior in its chemical industry in 1929. He widened the area of his research, adding to it the chemistry of higher terpenes and steroids in 1934. In collaboration with A.F.J. Butenandt, he started to study male sex hormones, established the structure of androsterone, which he managed to synthesize from cholesterol.
He also defined the structure of testosterone, and synthesized this compound as well. The most brilliant period of his professional career started with his work at ETH (Eidgenössische Technische Hochschule) in Zurich, when he made the laboratory he headed become one of the most recognized ones in the world.
Ruzicka received the 1939 Nobel Prize in Chemistry for his work showing that terpenes and some other large organic molecules are comprised of multiple units of isoprene, and for the synthetisation of the androsterone.