He was born into a well-off family. His father Karel Hannauer Sr. built a successful construction company in Prague-Nusle. Karel Hannauer Jr. studied architecture at the Prague Technical University (Pražská technika). After graduating from architecture, he devoted himself to publishing and study trips around Europe. Upon his return, he designed mostly apartment buildings in the family business. After the death of his father in 1931, Karel Hannauer Jr. continued to run the family business together with his uncle. In 1947 he was appointed associate professor of the Slovak University of Technology (Slovenská vysoká škola technická) in Bratislava. From 1955 to 1959 he lectured at the Czech Technical University (ČVUT) in Prague.