He was trained in biology by herpetologist Oskar Boettger (1844-1910) and malacologist Wilhelm Kobelt (1840-1916). From 1911 to 1936 he was a curator of invertebrate zoology at the Senckenberg Museum in Frankfurt am Main. On June 30, 1936, he was removed from his position at the Senckenberg Museum by the Nazis. From 1938 to 1959 Haas was curator at the department of lower invertebrates at the Field Museum of Natural History in Chicago.
Haas' specialty involved the study of land and freshwater snails, as well as research of the family Unionidae (freshwater mussels). He performed extensive field investigations in Norway (1910), Pyrenees, Spain, France (1914–19), southern Africa (1931–32; as part of the Hans Schomburgk expedition) and the Americas (Brazil, Bermuda, Cuba, Canada).
Taxa named in honor of Fritz Haas include:
- Cipangopaludina haasi (Prashad, 1928)
- Hans Morgenstern, Anton Pelinka "Jüdisches Biographisches Lexikon: Eine Sammlung von bedeutenden Persönlichkeiten jüdischer Herkunft ab 1800"
-  University of Michigan Museum of Zoology, Family Unionidae
- Solem A. (1967). "New molluscan taxa and scientific writings of Fritz Haas".Fieldiana 53(2): 71-144.
- Illinois Natural History Survey (biography of Fritz Haas)