In 1895 he earned his doctorate from the University of Vienna, and subsequently became an assistant to Franz Serafin Exner (1849–1926).
In 1907 he founded a seismological observatory at the physical institute in Graz, and during the same year was awarded with the Ignaz Lieben Prize for his work on the propagation of seismic waves.
In a mine-shaft at Příbram he was able to differentiate between long-distance earthquakes and local microseismic activity with the use of seismometers.
Also, he was the first scientist to solve the problem involving the refraction of seismic rays in spherical layers.
The term Benndorfscher Satz (Benndorf's relationship) is used to describe the constancy of the ray parameter across the spherical layers.