Kretzoi studied Arts and natural sciences at the then Pázmány Péter University, Budapest from 1925 to 1929. While still a student, he worked as a volunteer at the Geological Institute of Hungary.
In 1930 he gained a PhD in Palaeontology, Geology and Geography from the University of Pécs. In 1933 he commenced work with the "Hungarian-American Oil Inc" as a geologist and geophysicist. He remained at Hungarian-American Oil until the outbreak of the Second World War. Kretzoi moved to the National Museum of Hungary where he was curator of the Mineralogy and Paleontology departments until
he began work at Geological Institute of Hungary in 1950. Kretzoi was the director of the Geological Institute of Hungary from 1956 to 1958. From the mid-1960s he led the "digs" at Rudabánya where a number of Anthropoid fossil remains were discovered.