In 1906, he served as secretary for Naturforschender Verein in Brno, which was the society through which Gregor Mendel published his papers.

A socialist, Iltis spent much of his time from 1930 to 1938 combating the racist biology (eugenics) of the Nazis.

[1] He was a key organizer and host of the 1932 Brno congress of the World League for Sexual Reform.

With the help of Franz Boas and Albert Einstein and the Emergency Committee in Aid of Displaced Foreign Scholars, the Iltis family received a United States visa in the fall of 1938.

Initially, he taught for 5 weeks at the International School,[3] run by Peter Ray Ogden.

Following a chance meeting with Dean Edward Alvey in the grocery store, he was offered a professorship in biology at Mary Washington College in Fredericksburg, Virginia, where he taught for approximately 12 years.